Coffee Lake i7 -- 6 cores?

[itdk92]

Given Apple's history of not cannibalizing product lines, I don't see any logical reason why Apple would release a 6 core iMac give the Pro won't even start shipping close to 2018

You might have wanted to say “Given Apple’s history of often cannibalizing product lines..”

 

[fathergll]

You might have wanted to say “Given Apple’s history of often cannibalizing product lines..”

How so? 750 billion dollar tech company that offers only 2 different desktop computers (Mac Pro and Mac Mini for the last 10+ years). They don't even sell a middle of the pack desktop computer unless you want an all-in-one or laptop. Its not like Apple has been guilty of offering too many options.

 

[itdk92]

How so? 750 billion dollar tech company that offers only 2 different desktop computers (Mac Pro and Mac Mini for the last 10+ years). They don't even sell a middle of the pack desktop computer unless you want an all-in-one or laptop. Its not like Apple has been guilty of offering too many options.

Differentiation and options has little to do with cannibalizing products.

You might even sell only two products, but still being cannibalizing one of them.

They did this with iOS with both iPad and iPod, and certain models of iPhone (see iPad mini or iPod, to name two).

Of course there is no chance they are going to cannibalize a new shiny product.

But remember segmentation is also done by e.g price

 

[Jack Burton]

I'm curious as to whether or not Coffee Lake will require a new chipset.

Some say it is 1151 version 2 with a new chipset, and some say it is just 1151 and may use the existing chipset.

If 1151 with the existing chipset, then that could mean some enterprising people could try installing an i7-8700K or something in an existing Kaby Lake iMac.

The intel forums and 8700k reviews all say it requires the new chipset. I'd love to drop an 8700k in a new iMac, but I don't think it would handle the increased heat very well.

 

[Icaras]

What does outward design matter? I'd take a much-faster computer in a 1985 Zenith TV shell, if it speeds up my productivity.

Not to turn this discussion into a subjective matter, but design does matter a great deal to me as I purchased the 2012 iMax partly because of the design change and likewise, it has also been a deal breaker for me to withhold on a new purchase.

The day Macs are housed in Zenith TV shells is the day part of Apple’s core philosophy has died, and is also the day I’ll probably leave Apple.

 

[Appleaker]

Not to turn this discussion into a subjective matter, but design does matter a great deal to me as I purchased the 2012 iMax partly because of the design change and likewise, it has also been a deal breaker for me to withhold on a new purchase.

The day Macs are housed in Zenith TV shells is the day part of Apple’s core philosophy has died, and is also the day I’ll probably leave Apple.

A reason not to care for design refreshes is all the things that come with it for Apple. For the iMac the main concern there (for me at least) is a lack of upgradeable ram despite the RAM being slotted, similar to the iMac Pro.

 

[cynics]

Given Apple's history of not cannibalizing product lines, I don't see any logical reason why Apple would release a 6 core iMac give the Pro won't even start shipping close to 2018

I know the topic has gone far past this point but on this topic specifically.

Its quite the opposite. The iMac Pro is set to come in 8, 10 and 18 core variants. The business model is to place the top of the line iMac to where it makes me ask the question, "why not just get the iMac Pro?". In that business model people rarely ask the alternative because they've already found the added value in the Pro so it feels like a downgrade.

Secondly, to a real professional the iMac Pro will still offer things not available with the normal iMac. Going to a 6 core iMac and they lose more than just 2 cores (assuming we were talking about the base model). ECC memory up to 128gb, 4 usb 3 ports and 4 usb c ports, the ports in combination with a Xeon (or Xeon like, not sure what Apple is using) will offer more lanes as well, 10gb ethernet, etc.

If someone is swayed to by a normal iMac because it has 6 cores instead of an iMac Pro then they had no business considering the Pro in the first place.

 

[Jack Burton]

I know the topic has gone far past this point but on this topic specifically.

Its quite the opposite. The iMac Pro is set to come in 8, 10 and 18 core variants. The business model is to place the top of the line iMac to where it makes me ask the question, "why not just get the iMac Pro?". In that business model people rarely ask the alternative because they've already found the added value in the Pro so it feels like a downgrade.

Secondly, to a real professional the iMac Pro will still offer things not available with the normal iMac. Going to a 6 core iMac and they lose more than just 2 cores (assuming we were talking about the base model). ECC memory up to 128gb, 4 usb 3 ports and 4 usb c ports, the ports in combination with a Xeon (or Xeon like, not sure what Apple is using) will offer more lanes as well, 10gb ethernet, etc.

If someone is swayed to by a normal iMac because it has 6 cores instead of an iMac Pro then they had no business considering the Pro in the first place.

Nah, the 6 core is a sweet spot. The 8700k is a beast of a chip. It slays all in single threaded processes, and competes well in multithreaded. If the leaked geekbench numbers are to be believed, the 8 core iMac pro is coming in at 23,536 multithread score, 3826 single thread.

8700k gets 24,260 multi, 5773, and at lower TDP (95w vs supposed 140w on the xeon)

If apple offered it, I'd take an 8700k and sacrifice non upgradeable ecc ram in a heart beat. I think an 8700k based iMac would turn people away from the iMac pro entry level in droves. I also don't know if the current iMac could cool the 8700k adequately, so My guess is it will never show up in the current iMac lineup's form factor, and will never show up in the pro.

Damn shame.

 

[cynics]

Nah, the 6 core is a sweet spot. The 8700k is a beast of a chip. It slays all in single threaded processes, and competes well in multithreaded. If the leaked geekbench numbers are to be believed, the 8 core iMac pro is coming in at 23,536 multithread score, 3826 single thread.

8700k gets 24,260 multi, 5773, and at lower TDP (95w vs supposed 140w on the xeon)

If apple offered it, I'd take an 8700k and sacrifice non upgradeable ecc ram in a heart beat. I think an 8700k based iMac would turn people away from the iMac pro entry level in droves. I also don't know if the current iMac could cool the 8700k adequately, so My guess is it will never show up in the current iMac lineup's form factor, and will never show up in the pro.

Damn shame.

Geekbench is fine point of comparison but there are too many variables right now comparing a rumored CPU to known reference on a Windows machine (memory clock affects Geekbench score and so does OS albeit 5%).

But lets say for example the 8700K was offered now in the normal iMac. By the time you match the specs to the iMac Pro's entry model (1tb SSD, 32gb RAM, keyboard with numeric pad) you are less then 1300 dollars away. With that 1300 dollars you'd sacrifice a ECC memory that is clocked higher, 2 cores, cooling system better suited for professional workloads, a GPU that is MUCH faster, TB ports, secure enclave ARM CPU for whatever its going to do (touchID, faceID?), 1080p camera, 10gb ethernet.

That price gap could narrow too depending on the feature set of a newly released iMac. I don't think Apples target audience (that will probably write the Pro off anyway) will be overly deterred by the difference in cost vs the difference in specs.

I agree that the current cooling system couldn't handle the 8700K though. However Apple has typically included the best consumer level CPU in their iMac 27" that was available at the time of release and that made sense (ex. 3770 was used since the 3770K was just unlocked which is pointless on a Mac and had a .1 faster base clock).

 

[Miguel Cunha]

For multi-core heavy applications. The Adobe Creative Suite might not see much benefit though, and in fact, could be slower in a lot of stuff as compared to the current i7 7700K for example.

That's one of the reasons why I moved away from Adobe, after so many years.
A lot of people I know did the same.
[doublepost=1508488171][/doublepost]

If thats the case Apple isn't the best choice for you.

There's more to the Mac than the exterior design.
I wouldn't move away from macOS.
I do see your point, though.

 

[Jack Burton]

Geekbench is fine point of comparison but there are too many variables right now comparing a rumored CPU to known reference on a Windows machine (memory clock affects Geekbench score and so does OS albeit 5%).

But lets say for example the 8700K was offered now in the normal iMac. By the time you match the specs to the iMac Pro's entry model (1tb SSD, 32gb RAM, keyboard with numeric pad) you are less then 1300 dollars away. With that 1300 dollars you'd sacrifice a ECC memory that is clocked higher, 2 cores, cooling system better suited for professional workloads, a GPU that is MUCH faster, TB ports, secure enclave ARM CPU for whatever its going to do (touchID, faceID?), 1080p camera, 10gb ethernet.

That price gap could narrow too depending on the feature set of a newly released iMac. I don't think Apples target audience (that will probably write the Pro off anyway) will be overly deterred by the difference in cost vs the difference in specs.

I agree that the current cooling system couldn't handle the 8700K though. However Apple has typically included the best consumer level CPU in their iMac 27" that was available at the time of release and that made sense (ex. 3770 was used since the 3770K was just unlocked which is pointless on a Mac and had a .1 faster base clock).

I'm absolutely willing to trade ECC ram and two thunderbolt ports and save more than $1300 (because I won't buy Apple ram on a machine where I can add it myself). As for the GPU, yeah, it's faster. But I'll have to add nVidia external GPUs to it anyway, so why waste the $$$?

I think Apple won't use the 8700k because it would perform better than the base pro at a lower price point. But I also think the 8700k is in that unique thermal spot that prevents Apple from using it it in the current iMac form factor, and they won't use it in the pro since it doesn't have the PCI lanes to handle 4 thunderbolt 3 ports.

But this is all just my insane speculation, which I enjoy too much!

For multi-core heavy applications. The Adobe Creative Suite might not see much benefit though, and in fact, could be slower in a lot of stuff as compared to the current i7 7700K for example.

In Puget system tests, the 8700k is faster than the 7700k in Photoshop, Lightroom, After Effects, and Premiere. But as you say, not by much in some apps! (looking at you, photoshop and after effects)


Photoshop:

Photoshop isn't the best at using a lot of CPU cores, so it is no surprise that the new Coffee Lake 8th Gen CPUs are not massively faster than the previous generation. The Core i7 8700K is still a very decent 9-14% faster than the Core i7 7700K, but it isn't 50% faster as some might have expected from the 50% increase in core count.

Premiere:

starting with the Core i7 8700K, we saw huge performance gains compared to the Core i7 7700K. A 31% gain when rendering previews and a 36% gain when exporting is a staggering increase in performance. Even warp stabilize was on average 24% faster than the Core i7 7700K! Live playback didn't improve much, but this makes the Core i7 8700K a terrific CPU for those on a budget.

After Effects (disappointingly, one of the least threaded adobe apps):

Averaging our results from both the RAM Preview and Final Render sections - but keeping the Cinema 4D rendering results separate - we get a clear look at how the new Core i7 8700K, Core i5 8600K, and Core i3 8350K perform in After Effects.

For general AE usage, these CPUs are terrific. The performance gains are not as large as we've seen in some other applications since AE isn't terribly effective at utilizing more than a handful of CPU cores, but the Core i7 8700K was a solid 9% faster than the Core i7 7700K. Even the Core i5 8600K did very respectably, coming in at 5% faster than the Core i7 7700K while also being $80 cheaper.

For 3D rendering, the new Core i3 and i5 CPUs are not that impressive but the Core i7 8700K did a fantastic job. This makes the Core i7 8700K a great CPU if you occasionally or rarely use the Cinema 4D renderer, although there are a number of other choices if you need even more 3D rendering performance.

No surprise that After effects is only 9% faster, but I'll take what I can get as CPU makers struggle.

Final Cut would fly on the 8700k. It's a good all around chip, giving the user a 10% jump in performance in most apps, and a lot of boost to some.

 

[EugW]

I'm absolutely willing to trade ECC ram and two thunderbolt ports and save more than $1300 (because I won't buy Apple ram on a machine where I can add it myself). As for the GPU, yeah, it's faster. But I'll have to add nVidia external GPUs to it anyway, so why waste the $$$?

I think Apple won't use the 8700k because it would perform better than the base pro at a lower price point. But I also think the 8700k is in that unique thermal spot that prevents Apple from using it it in the current iMac form factor, and they won't use it in the pro since it doesn't have the PCI lanes to handle 4 thunderbolt 3 ports.

But this is all just my insane speculation, which I enjoy too much!

Given that the iMac Pro is a niche product, I think Apple will put the 8700K in the 2018 iMac. They would sell far, far, far more of those than a much higher priced iMac Pro.

However, it's moot for me. I found the 7700K far too hot and noisy (periodically) for my liking so I returned it to get an i5 7600 instead, and I'm much happier as the machine is pretty much always silent. So for me, the most exciting development for 2018 would be a 65 Watt 6-core i5 model. I would never even consider the 8700K based on my experience with the 7700K, unless real world tests proved it was significantly less hot than the 7700K which seems highly unlikely. But then again, I don't have the same hardcore performance needs that some people may have.

Actually, what I'd like to see is the i7 8700 non-K in the 27" iMac or equivalent, but for some reason Apple never doesn't put these non-K i7 chips in those. They only put in the smaller 21.5" iMac, which is really irritating.

If the 2018 iMac is anything like the 2017 iMac, IMO the best chip overall for it in terms of my preferences might in fact be the i7 8700 non-K, at least on paper.

https://www.intel.com/content/www/us/en/products/processors/core/i7-processors/i7-8700.html

In Puget system tests, the 8700k is faster than the 7700k in Photoshop, Lightroom, After Effects, and Premiere. But as you say, not by much in some apps! (looking at you, photoshop and after effects)

I was specifically thinking about the 2D Adobe applications, but it's good to know at least there isn't a regression in performance. However, it should also be noted that Adobe applications tend to be better optimized on the Windows side (where those tests were done) than on the Mac.

So, while it may turn out that 8700K is indeed faster in all these apps on the Mac side too, there is no guarantee the improvements are by the same amount, and the improvements are already low on the Windows side for some of them.

 

[Jack Burton]

Given that the iMac Pro is a niche product, I think Apple will put the 8700K in the 2018 iMac. They would sell far, far, far more of those than a much higher priced iMac Pro.

However, it's moot for me. I found the 7700K far too hot and noisy (periodically) for my liking so I returned it to get an i5 7600 instead, and I'm much happier as the machine is pretty much always silent. So for me, the most exciting development for 2018 would be a 65 Watt 6-core i5 model. I would never even consider the 8700K based on my experience with the 7700K, unless real world tests proved it was significantly less hot than the 7700K which seems highly unlikely. But then again, I don't have the same hardcore performance needs that some people may have.

Actually, what I'd like to see is the i7 8700 non-K in the 27" iMac or equivalent, but for some reason Apple never doesn't put these non-K i7 chips in those. They only put in the smaller 21.5" iMac, which is really irritating.

If the 2018 iMac is anything like the 2017 iMac, IMO the best chip overall for it in terms of my preferences might in fact be the i7 8700 non-K, at least on paper.

https://www.intel.com/content/www/us/en/products/processors/core/i7-processors/i7-8700.html

Oh, I forgot about that chip. Isn't it also a 65w TDP? That might work really well. It might be quieter than the 7700k, and I already don't really mind that one in this iMac. It's basically on par with the 7700k in single thread, and a good chunk faster in multi. Nice balance. Lower TDP. Just a solid chip.

I was specifically thinking about the 2D Adobe applications, but it's good to know at least there isn't a regression in performance. However, it should also be noted that Adobe applications tend to be better optimized on the Windows side (where those tests were done) than on the Mac.

So, while it may turn out that 8700K is indeed faster in all these apps on the Mac side too, there is no guarantee the improvements are by the same amount, and the improvements are already low on the Windows side for some of them.

Is the difference between Mac and windows that bad? I honestly didn't notice that much in my old PC and old iMac.

 

[smoledman]

I bet we don't see Coffeelake 6-core iMacs until spring 2019. Apple wants to let the iMac Pro have the > 4 core processor field to itself for a year.

 

[cynics]

Given Apple's history of not cannibalizing product lines, I don't see any logical reason why Apple would release a 6 core iMac give the Pro won't even start shipping close to 2018

Only thing it would likely cannibalize is the product line (iMac Pro) itself. Upgrades on base models increases profit margins exponentially. That is one of the reasons they offer prepackaged tiers to begin with on the same product lines.

I can only use retail pricing but consider this. Going from a 3.8 ghz i5 to 4.2 ghz i7 is 200 dollars. However its actually 200 dollars + 250 dollars (the original cost of the 3.8ghz i5 you no longer get). Going from a 2tb fusion is 600 dollars. However its 600 dollars plus the 100-150 dollars (128gb SSD and 2tb HDD). RAM...well we already know how Apples RAM prices are...

There is a very good chance from a financial perspective Apple would prefer you to max out an iMac 5k than buy a base iMac Pro.

There is something to be said about product lines doing well in general especially when it comes to shareholders but they've done a good job setting the iMac Pro into a niche market designed for professionals exclusively. And with so many non professionals buying them (as likely intended) they will easily be able to say their expectations were exceeded to shareholder meetings.

 

[CWallace]

I bet we don't see Coffeelake 6-core iMacs until spring 2019. Apple wants to let the iMac Pro have the > 4 core processor field to itself for a year.

The iMac Pro is more than just it's CPU, however.

And while PassMark scores between the i7-8700K and W-2135 are similar, the Xeon has 1MB of L2 cache per core whereas I believe Coffee Lake shares 256KB of L2 cache across all cores so if you are doing something that can make use of the L2 cache, the Xeons should see a nice performance boost.

 

[EugW]

I thought I was forced to buy my new iMac in 2017 due to work budgetary reasons, but it turns out I could have bought in 2018 due to my work circumstances changing. Oh well, I'm satisfied with my i5-7600 I'm typing on right now. No 6-core iMac for me.

The funny part is that I will be upgrading my Windows 10 PC to 6-core soon... but that will only bring it to roughly about my 2010 i7 iMac's speeds. My Windows PC has a circa 2009 AMD Athlon II X3 435 2.9 GHz 3-core CPU, which is roughly moderate desktop Core 2 Duo performance, but I have ordered an AMD Phenom II X6 1055T 2.8 GHz 6-core which is roughly twice as fast. I believe that after my last firmware update, the 6-core is actually a drop-in replacement for the 3-core. Hopefully this works to keep my Windows PC going for several more years.

 

[sublunar]

It would be very easy for Apple to put Coffee Lake 6 core CPU into the ordinary iMac - the CPUs are available right now and I can't see Apple trying to hide the 6 Core CPUs behind a BTO option.

All Apple have to do is select a suitable GPU (AMD Vega Mobile, presumably) and refresh. The iMac Pro is priced into a completely different segment and Apple just have to decide when to update - June would make it a year since the last update.

The only worry people should have now is that Apple could now seal the RAM trapdoor on the 27" iMac like they've done with the iMac Pro, especially if they just use the iMac Pro as a template for the next 27" iMac.

The only 2 international issues they have to consider is the relative weakness of the US Dollar (meaning UK prices might get a cut this summer!) but pushed up against high demand for GPUs driving the price up (meaning UK prices might not get that cut this summer!)

 

[EugW]

It would be very easy for Apple to put Coffee Lake 6 core CPU into the ordinary iMac - the CPUs are available right now and I can't see Apple trying to hide the 6 Core CPUs behind a BTO option.

Here we go. These are the Coffee Lake CPUs I was most interested in. They just showed up on Intel's database:

https://www.anandtech.com/show/12392/intel-adds-new-cfl-cpus-to-database

Core i5-8600 65 Watt - 6 core 6 thread
Core i5-8500 65 Watt - 6 core 6 thread

I betcha Apple is waiting for these for the 27" iMac. AFAIK, they're not going to come out until Valentine's Day. I personally find those more enticing than the previously released ones:

Core i7-8700K 95 Watt - 6 core 12 thread
Core i5-8600K 95 Watt - 6 core 6 thread
Core i5-8400 65 Watt - 6 core 6 thread

The Core i5-8700 65 Watt - 6 core 12 thread would be nice, but I suspect Apple won't put that in the 27" iMac, just the 21.5" iMac, if the 2017 models are any indication.

 

[Glmnet1]

With the specs of these CPU I could see Apple removing the i7 from the iMac with the next refresh, creating a bigger difference with the iMac Pro and lowering the max TDP. Those 6/12 i7 seem dangerously close to the 8/16 Xeons. We'll see.

I wouldn't mind personnaly, I'll be getting the base i5 and those 6 fine cores

 

[sublunar]

With the specs of these CPU I could see Apple removing the i7 from the iMac with the next refresh, creating a bigger difference with the iMac Pro and lowering the max TDP. Those 6/12 i7 seem dangerously close to the 8/16 Xeons. We'll see.

I wouldn't mind personnaly, I'll be getting the base i5 and those 6 fine cores

The iMac Pro is a well loaded machine - if you bump an iMac to 32Gb RAM, 1Tb SSD and i7 CPU it's within a few hundred dollars of the base iMac Pro. In that respect Apple don't need to drop an i7 from the options list. They already make big profit whenever anyone specs it now. Apple probably save on the GPU which won't be anything near as powerful as Vega 56 and 64 in the iMac Pro.

There's still a chance that Apple will close the upgrade door for RAM in the 27" iMac by using the same cooling solution as iMac Pro which eliminates the RAM access door which people have valued.

It would be a bittersweet price to pay for the possibility of having a 6 core/12 thread iMac.

 

[CWallace]

Core i5-8600 65 Watt - 6 core 6 thread
Core i5-8500 65 Watt - 6 core 6 thread

I betcha Apple is waiting for these for the 27" iMac. AFAIK, they're not going to come out until Valentine's Day. I personally find those more enticing than the previously released ones:

Core i7-8700K 95 Watt - 6 core 12 thread
Core i5-8600K 95 Watt - 6 core 6 thread
Core i5-8400 65 Watt - 6 core 6 thread

Yes it seems logical based on previous releases that the i5-8600 will be the standard and the i5-8600K and i7-8700K will be the upgrade options.

The Core i5-8700 65 Watt - 6 core 12 thread would be nice, but I suspect Apple won't put that in the 27" iMac, just the 21.5" iMac, if the 2017 models are any indication.

I doubt the 21.5" would get it as that is the "value" model with ~$200 CPUs not ~$300. As such, I expect the 21.5" will get the i5-8400 as standard with the i5-8500 as the upgrade option.

With the specs of these CPU I could see Apple removing the i7 from the iMac with the next refresh, creating a bigger difference with the iMac Pro and lowering the max TDP. Those 6/12 i7 seem dangerously close to the 8/16 Xeons. We'll see.

Again, the iMac Pro is more than just it's CPU. Even if the i7-8700K benches as well as or better than the W-2140B, the iMac Pro still has ECC RAM, dual SSDs, more ports and a better GPU (even if the 2018 model gets Vega RX). And Apple has thermal headroom in the iMac Pro so they could raise the base and Turbo frequency to the same as the W-2145.

 

[deewt]

I'm patiently waiting for this years refresh after deciding not to jump on the kaby lake model last year.
It would be SUCH a let down if they don't make the i7 8700K available to the 27" model.

With the recent news updates from Intel, I wonder if we might see an announcement for iMac sooner than later? (THIS did get me excited last year)

 

[EugW]

Yes it seems logical based on previous releases that the i5-8600 will be the standard and the i5-8600K and i7-8700K will be the upgrade options.

The current 27" has the base as the i5-7500, with upgrades being the i5-7600, i5-7600K, and i7-7700K.

I doubt the 21.5" would get it as that is the "value" model with ~$200 CPUs not ~$300. As such, I expect the 21.5" will get the i5-8400 as standard with the i5-8500 as the upgrade option.

The current 21.5" has the i7-7700 as an upgrade option, with the base Retina 4K model being the i5-7400.

 

[joema2]

With the specs of these CPU I could see Apple removing the i7 from the iMac with the next refresh, creating a bigger difference with the iMac Pro and lowering the max TDP. Those 6/12 i7 seem dangerously close to the 8/16 Xeons. We'll see....

You are right, there is a potential dilemma. The top-spec 2017 iMac is already "nipping at the heels" of a 8-core or even 10-core iMac Pro on certain workflows. This is due to several factors, e.g, software doesn't properly harness multithreading or 4k H264 where the iMac has an advantage via Quick Sync (although the iMP is much faster than the 2013 nMP).

For pure GPU-intensive workflows or efficiently-written multi-threaded code, the iMP has a big advantage. The iMac Pro is really quiet under sustained loads. That by itself is a big attraction for some.

OTOH if the next top iMac uses the i7-8700K, that adds two more cores. The proportional speedup advantage going from 4 to 6 cores is large -- probably more than going from 10 to 18 cores -- since Amdahl's law caps speed up at high core numbers: https://en.wikipedia.org/wiki/Amdahl's_law

The i7-8700K has Quick Sync so that's a big advantage for video editing software which uses that. Right now that's mostly FCPX although I think Edius also uses it. Maybe someday Adobe will use this on Premiere for Mac.

FCPX 10.4 running on the iMac Pro is Apple's first attempt to use AMD-based hardware acceleration for video encode/decode. It works pretty well but there are some anomalies such as 4k H264 export seems slower than the 2017 iMac, but 1080p is faster. I suspect this is due to the "version 1" implementation. The AMD Vega hardware itself supports H264 encode/decode up to 3840x2160 at 60 fps, and 4096x2160 at 30 fps. This is described on page 13 & 14 of the AMD whitepaper "Radeon’s next-generation Vega architecture": http://radeon.com/_downloads/vega-whitepaper-11.6.17.pdf

However I can't see Apple artificially limiting the next iMac by removing the i7 option. The iMP is too specialized with things like ERCC memory.

It is conceivable they might lift the iMP cooling system for the next iMac, which might or might not remove the memory hatch on the rear. The ERCC sticks are larger, so that's another reason why the hatch was removed on the iMP.

Looking out 2-3 years, Apple must either continue upgrading the iMac Pro or the iMac will definitely intrude on that space, just like it did the Mac Pro. However this issue exists with all manufacturers having multi-tier product lines. It's just something they must face. Who was it that said "if you aren't willing to cannibalize your own products, your competitors will do it for you"?