iMac 27" - i5 (3.8GHz) or i7 (4.2GHz)

[iliasp]

So is it safe to say that gpu by the time they share the heatsink with the cpu does play an important role on these increased values in temp? And noise?
I have a base i5 3.4 with 570 GPU, dead silent no matter what and was thinking to replace the cpu with an i7 from ebay

 

[EugW]

I have purchased three current gen 27" iMacs; 3.5 w/ 575, 3.8 w/ 580, and 4.2 w/ 580. Noise is a big deal to me. All of these iMacs are quiet until they start to hit 100 degrees C at which point the fans become audible. The 3.5GHz iMac rarely (almost never) hits 100C and thus stays silent 99.9% of the time. The 3.8GHz iMac with the 580 will get just up to 100C and hand out around 95-98C. The 580 does get a bit warmer and you'll hear the fans kick off from time to time because of the GPU. The 4.2GHz iMac would hit 100C doing odd tasks like updating a bunch of Dropbox files or on random webpages.

So, I stuck with the 3.8GHz machine with the 580. I don't miss hyper-threading too much, I get the 580, and I don't have to endure the high-pitched whine of the iMac with the i7.

Thanks, that's excellent information. Being a recipient of one of the earliest 2017 i7 4.2 iMacs, I didn't have useful information such as this at my disposal.

I got my i7 right away, and then in the first few days I started getting annoyed by the noise of the i7's fan coming on at times when I wasn't expecting it.

I wasn't sure what the behaviour of the i5-7600k 3.8 would be but because it is rated as a high TDP chip (at 91 Watts) and because I didn't really need the 580 GPU, I ended up just getting the i5-7600 3.5 (at 65 Watts) with 575. The 3.5 is sufficient for me but I found out later that despite the TDP rating, the 3.8 behaves closer to the i5 3.5 than the i7 4.2, and in some tests almost identical in terms of fan response, so the 3.8 might have been fine for me too.

However, it is good to know from your testing that in some cases even with regular usage the 3.8 with 580 does indeed run hotter than the 3.5. It probably is partially the luck of the draw though.

I'm curious though. When you said "the 580 will get just up to 100C and hand out around 95-98C", what were you doing?

 

[topgunn]

I think if you switched out the 3.4GHz i5 for the 4.2GHz i7, you would no longer have a dead silent iMac. From my experience, the CPU has more to do with high temps than the GPU.

 

[EugW]

So is it safe to say that gpu by the time they share the heatsink with the cpu does play an important role on these increased values in temp? And noise?
I have a base i5 3.4 with 570 GPU, dead silent no matter what and was thinking to replace the cpu with an i7 from ebay

That would be crazy IMO.

And yes, it's because of the CPU. People on the PC side have been complaining about just how fast the temps ramp up on the i7 (and not the i5 chips). Many of the loudest complainers are overclockers, but the telling part is that Intel responded saying yes the i7 ramps up temp quickly and this is normal behaviour and they should stop overclocking... despite the fact this is an unlocked chip that caters to the overclocking crowd.

IOW, Intel admits the i7 is a very hot chip, saying it's normal for it.

 

[topgunn]

When you said "the 580 will get just up to 100C and hand out around 95-98C" though, what were you doing?

Initially, I was using Prime 95 on each iMac to isolate the heat generated by the CPU from the heat generated by the GPU. The two i5 iMacs stayed quiet while the i7 iMac had the fans going at high speed. Once I saw that the 3.8GHz i5 stayed quiet running Prime95, I was sold. Now, the fans do come on from time to time while gaming but not dissimilar from my 2013 iMac and still much quieter than the 2017 iMac with the i7.

For what its worth, I didn't notice much difference between the 3.5 and 3.8. Were it not for the extra Video RAM of the 580, I would have stayed with the 3.5. I think you made a good choice.

 

[EugW]

BTW, with the i5-7600 3.5 with 4 GB 575 hooked up to an additional external 2560x1440 monitor, I notice no significant difference in OS responsiveness for 2D desktop usage. (I use a 2010 27" iMac as the external monitor.)

I don't know if there would be any significant slowdown with an additional 5120x2880 monitor, because I don't have one to test. I suspect though unless I'm gaming or doing 3D rendering or something, the 4 GB and 575 GPU are more than enough.

 

[Miguel Cunha]

Some of the 2018 i5 machines will be 6-core. This will change the equation.

No doubt, they will be game changers, although six cores without HT, still falls behind for cores with it.
Anyway, I was referring to current models, which are in SirApple's crosshairs.

 

[Mac32]

I have purchased three current gen 27" iMacs; 3.5 w/ 575, 3.8 w/ 580, and 4.2 w/ 580. Noise is a big deal to me. All of these iMacs are quiet until they start to hit 100 degrees C at which point the fans become audible. The 3.5GHz iMac rarely (almost never) hits 100C and thus stays silent 99.9% of the time. The 3.8GHz iMac with the 580 will get just up to 100C and hand out around 95-98C. The 580 does get a bit warmer and you'll hear the fans kick off from time to time because of the GPU. The 4.2GHz iMac would hit 100C doing odd tasks like updating a bunch of Dropbox files or on random webpages.

So, I stuck with the 3.8GHz machine with the 580. I don't miss hyper-threading too much, I get the 580, and I don't have to endure the high-pitched whine of the iMac with the i7.

Thanks, that's very useful information. So the i7 will basically rev up the fan by simply browsing the web? Wow, that's not good. This has never happened even once with my late 2012 i7 after almost 5 years of use. Hmm...

 

[EugW]

No doubt, they will be game changers, although six cores without HT, still falls behind for cores with it.

No it doesn’t.

The i5-8600K 3.6 GHz is faster than the i7-7700K 4.2 GHz in multithreaded applications. eg. Cinebench R15 scores higher on the 8600K.

 

[J.Gallardo]

No it doesn’t.

The i5-8600K 3.6 GHz is faster than the i7-7700K 4.2 GHz in multithreaded applications. eg. Cinebench R15 scores higher on the 8600K.

Yes, it seems.
But Apple is not fast at adopting new processors. Actual iMacs are possibly the last desktops in market to offer Intel KabyLake cpus. In laptops was the same.
I know that implementing new required mainboard could be technically easy, but the mastodontic Apple production chain uses to innovate at a slow, safe pace.
Perhaps “next summer” is the earliest logical time when we should expect a change in iMac line.
The iMac Pro is coming, and needs the spotlight...
And no sign of traffic in the web from Apple machines with those new cpus!
Anyhow, now that Apple sells watchbands and all that fancy stuff, I’m getting lost finding a pattern in their computers department. :-/

 

[EugW]

I expect the 2018 iMacs to come out in summer, a couple of months before macOS 10.14 is released.

Then my prediction is when macOS 10.14 is released, iTunes will bring 4K DRM'd video to Macs, limited to the 2017 and 2018 Macs only. Then Netflix 4K will follow, again only on 2017 and 2018 Macs.

 

[smartbot]

The i7 is worth it in my opinion. I had a previous iMac with the i5 and I had to upgrade a few years later. The i7 will last you longer...

 

[Mac32]

I'm seeing that the six core i5 8600k, that will probably be the update for the 2018 iMac is 95W. This versus the preset i7 top CPU, which is only 91W, and is already pushing the limit of the iMac thermals (people are reporting the only web browsing will activate the fans with 2017 i7 CPU). Apple really needs to improve the fan and heatsink system for the iMac, or the next 2018 model is gonna be a hot and noisy machine.

 

[EugW]

I'm seeing that the six core i5 8600k, that will probably be the update for the 2018 iMac is 95W. This versus the preset i7 top CPU, which is only 91W, and is already pushing the limit of the iMac thermals (people are reporting the only web browsing will activate the fans with 2017 i7 CPU). Apple really needs to improve the fan and heatsink system for the iMac, or the next 2018 model is gonna be a hot and noisy machine.

It’s likely that the 91 W i7-7700K heats up quicker than the 95 W i5-8600K.

 

[Huddy]

It will be interesting to see whether Apple will make changes to the existing iMac cooling solution if they do offer Coffee Lake. From reading reviews the current system would most likely handle the 8600K much the same as the 7700K, but that 8700K gets mighty toasty when it's worked out, with some sites concluding that if you do any taxing rendering sessions or suchlike work on a consistent basis you'd be better off choosing an alternate cooling solution to air such as closed loop water cooling.

 

[Miguel Cunha]

The i5-8600K 3.6 GHz is faster than the i7-7700K 4.2 GHz in multithreaded applications. eg. Cinebench R15 scores higher on the 8600K.

Does benchmarking applications can be deceiving.
What about real world 4K video editing?
Which of them will perform better?

 

[wardie]

Good decision on the SSD. It´s faster and much simpler than Fusion. I also recommend only to use it as System disc, just for macOS and applications. Buy an external storage, preferably a RAID, with no less than 7200 RPM and configure it to RAID 0, for maximum speed, or if it has at least 4 drives, to RAID 5, for a balance between speed and redundancy - If one of the drives fails, you're still safe and can replace it, without any loss of data.
Hope this helps.

Or if you want some serious external speed go with an external SSD RAID 0 setup but you’ll need to use Thunderbolt best or USB3 to benefit from the speed, plus a RAID box/controller that is speedy to leverage the SSDs properly. Really depends on your cost appetite and need.

 

[Miguel Cunha]

Hi Miguel, thank you for your response

I think I will end up with the i7 to make the computer a bit more future proof.

In terms of the setup with an external storage; that could a smart setup to make sure that everything runs smoothly. I also plan to install Windows on bootcamp.

Any recommendation for external storage? I guess I would like something in the line of 1-2TB.

Thanks

//SirApple

Sorry for the late response, but I failed to see your query.
Again, it depends on what you need in capacity and speed.
Check out this drive, as I think it will suffice your needs at a good price. I use a former model for over 4 years and it never failed, so very robust. You can opt for other RAID models.
You can also check this model, just to have an idea.

Hope this helps.

 

[EugW]

Does benchmarking applications can be deceiving.
What about real world 4K video editing?
Which of them will perform better?

Dunno for editing but it would depend upon the GPU, and for video encoding the 8600K would probably at least equal the 7700K and maybe would beat it.

Like Cinebench, video encoding is something that can easily max out all cores. The performance increases linearly with number of cores. The improvement from hyper threading is much, much less.

 

[Miguel Cunha]

Or if you want some serious external speed go with an external SSD RAID 0 setup but you’ll need to use Thunderbolt best or USB3 to benefit from the speed, plus a RAID box/controller that is speedy to leverage the SSDs properly. Really depends on your cost appetite and need.

Redundancy is a must in these workflows. I prefer to sacrifice some speed, and have a safety net in case a drive fails.
SSDs are the ideal solution for speed, but you have two drawbacks: capacity and price.
You can have a hybrid solution, SSDs just for the footage you're working with and another kind of storage, depending on purpose, it could be HDD, or for archiving, I would go for this, since it lasts foro ver 100 years.
[doublepost=1513262574][/doublepost]

Dunno for editing but it would depend upon the GPU, and for video encoding the 8600K would probably at least equal the 7700K and maybe would beat it.

For video encoding, unfortunately, yes, as software makers keep parallel processing to their server solutions. As for video editing, Apple just released Final Cut Pro 10.4, with support up to 36 threads, so clearly the i7 would perform better.
Also, generally better CPUs, offer options for better GPUs, so it would be another win.

 

[EugW]

Redundancy is a must in these workflows. I prefer to sacrifice some speed, and have a safety net in case a drive fails.
SSDs are the ideal solution for speed, but you have two drawbacks: capacity and price.
You can have a hybrid solution, SSDs just for the footage you're working with and another kind of storage, depending on purpose, it could be HDD, or for archiving, I would go for this, since it lasts foro ver 100 years.
[doublepost=1513262574][/doublepost]
For video encoding, unfortunately, yes, as software makers keep parallel processing to their server solutions. As for video editing, Apple just released Final Cut Pro 10.4, with support up to 36 threads, so clearly the i7 would perform better.
Also, generally better CPUs, offer options for better GPUs, so it would be another win.

More cores do better with more threads than less cores with HT do. That was the whole point of my post. The 8600K provides 50% more cores than the 7700K. The 8600K with all 6 cores active runs at 4.1 GHz. Since encoding speed essentially scales linearly with number of cores, it’s roughly like having a hypothetical 24.6 GHz CPU.

In contrast, the 7700K has 4 cores running at 4.4 GHz. That would similar to a 17.6 GHz single core CPU. In video encoding HT will offer approximately a 10-20% performance improvement. If we are generous and say it’s 20%, that’s 17.6 x 1.2 = 21.1, which means the slower clocked 6-core 8600K still beats it.

As for the 8600K iMac’s GPU, it will likely be available with the best GPU Apple will offer in 2018, which is undoubtedly going to be better than what the 7700K currently ships with.

---

Below is a real world test. The 8600K easily beats the 7700K in both h.264 and h.265 video encoding. (Lower = faster)

https://www.techpowerup.com/reviews/Intel/Core_i5_8600K/6.html

Interestingly, in this test even the lowly i5-8400 beats the 7700K. What makes this very interesting to me is that the 8400 a 65 Watt TDP chip.

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My calculations above suggest that the 8600K might be about 16%-17% faster than the 7700K. According the graphs above, the actual difference is more like 12%-13% but not too far off the hypothetical guestimates.

 

[jon08]

More cores do better with more threads than less cores with HT do. That was the whole point of my post. The 8600K provides 50% more cores than the 7700K. The 8600K with all 6 cores active runs at 4.1 GHz. Since encoding speed essentially scales linearly with number of cores, it’s roughly like having a hypothetical 24.6 GHz CPU.

In contrast, the 7700K has 4 cores running at 4.4 GHz. That would similar to a 17.6 GHz single core CPU. In video encoding HT will offer approximately a 10-20% performance improvement. If we are generous and say it’s 20%, that’s 17.6 x 1.2 = 21.1, which means the slower clocked 6-core 8600K still beats it.

As for the 8600K iMac’s GPU, it will likely be available with the best GPU Apple will offer in 2018, which is undoubtedly going to be better than what the 7700K currently ships with.

---

Below is a real world test. The 8600K destroys the 7700K in both h.264 and h.265 video encoding. (Lower = faster)

https://www.techpowerup.com/reviews/Intel/Core_i5_8600K/6.html

View attachment 742001

View attachment 742002

Interestingly, in this test even the lowly i5-8400 beats the 7700K. What makes this very interesting to me is that the 8400 a 65 Watt TDP chip.

Well, as far as I can see from those benchmarks the 8600K is less than 15% faster than 7700K. That imo is far from “destroying” it.

 

[EugW]

Well, as far as I can see from those benchmarks the 8600K is less than 15% faster than 7700K. That imo is far from “destroying” it.

OK. I have changed it to say "easily beats".

The point is I don't think Miguel understands that HyperThreading is no substitute for actual cores, esp. in video encoding.

The 6-core i5 chips in 2018 are indeed a game changer. You'll have lowest end 65 Watt 6-core i5 chip (8400) beating the top-of-the-line 91 Watt i7 chip (7700K) from the year before in video encoding.

 

[SirApple]

Sorry for the late response, but I failed to see your query.
Again, it depends on what you need in capacity and speed.
Check out this drive, as I think it will suffice your needs at a good price. I use a former model for over 4 years and it never failed, so very robust. You can opt for other RAID models.
You can also check this model, just to have an idea.

Hope this helps.

Thank you Miguel!

The Pegasus3 feels like overkill of my needs and what I had in mind in terms of budget

The AV PRO 2 seems very big? And is it only offered as HDD or is it also as SSD?

I'd prefer something smaller, found this from the same store, would that also work?

Would it work/be smart to put the Windows bootcamp on an external drive or is it better to put it on the internal and then just put all the games/files on the external?

 

[propower]

6+ months of owning the i5 3.8 with 1TB SSD for Multitrack audio recording, mixing and light video editing for music videos (AVCHD 1080P). Performance is stellar across the board. Never hear the fan unless encoding a >4 minute music video. Then maybe 1800rpm - no issue. Like some others - I too owned the 3.4 i5 and the 4.2 i7. The 4.2 i7 ran 20 to 30 degreesC hotter for normal non stressful tasks than the i5s. It also hit the fans for little things and had sustained full speed fans for all encoding over 30 seconds long. In my experience, The i5s are almost indistinguishable in single core tasks from each other and the i7. In multicore the i7 is clearly faster though for the video encoding I was doing 20% faster was all I saw over the 3.4 i5. If one needs the speed on video or image processing tasks the i7 makes sense. If music projects would not fit in my i5 I would have kept my 6 core Mac Pro. Like some others - I care not about future proofing anymore. If the machine can't fit my growing needs I will replace it. FWIW - I up speced every machine for the last 20 years. Only in 1998 was it necessary.