W-3300 series indeed comes with PCIe 4.0, for example,
32-core Xeon W-3365.
Personally I won't expect PCIe 4.0 something to be excited about. Workloads such as 4K video production (perhaps the most common & demanding workload a Mac Pro faces in daily operations) could hardly see benefit both GPU & storage performance wise.
In some context it will. First, MPX Duo modules. With PCI-e v3 you have two. x16 PCI-e v4 GPUs trying to share a single x16 PCI-e v3 backchannel to the CPU ( so that is about a x8 v3 split between them). With PCI-e v4 you would pragmatically have a x16 v3 split between them. The DUO would be no worse than the single PCI-e v4 x16 GPU modules in that respect. It is going to be much easier to actually get the line speed ups.
Second, Afterburner's inputs and output are two vastly different sizes.
PCI-e v3 x16 --> 128Gb/s.
One uncompressed 10 bit color 8K 60Hz data stream. -->. 62 Gb/s.
" " " @ 30Hz data stream --> 30 Gb/s.
4 * (the 30Hz stream ) --->. 120 Gb/s.
Technically not completely saturating the x16 input, but if have to walk and chew gum at the same time ( where something else from CPU also needs substantive bandwidth). Afterburner probably caps out at four , highest fidelity, 8K streams for a reason other than the FPGA ran out of "horsepower" .
PCIe 4.0 is a nice bump in the spec. Due to prolonged lifespan of v3.0, PCIe 4.0 will be very short lived and be replaced by PCIe 5.0 in workstations in 2023. PCIe 5.0 is something to be very excited about in add-in card markets/applications in general. IMO, PCIe 5.0 is a huge uncertainty if Apple will tit-for-tat follow the PC industry trend.
Will Apple even. tit-for-tat for. PCI-e v4 at more than x1 bundles over the short term? Pretty good chance that Apple doesn't want to go there and that an Intel model that does helps "kick the can" to 3rd or later generation M-series.
If Apple is out to kill off 3rd party dGPUs (if not dGPUs altogether ) then that will take lots of 'air' out of the sails to more rapid adoption of the versions past v4.
One of the immediate benefits of the new Ice Lake Mac Pro is the memory sub-system, both capacity & performance wise. All SKUs come with 8 memory channels (instead of 6 in MacPro7,1) and support max capacity of 4TB (instead of 0.7-1TB in MacPro7,1).
Pretty doubtful Apple is going to add more DIMM slots to the motherboard. The cheapest , quickest path forward for them would be to either keep the 12 DIMM slots have now with a different controller to slot mapping. ( e.g., straight 1-to-1 mapping for 4 slots and 2-to-1 mapping for another 4 slots ( 4 + 2*4 = 12 ). Akin to the 3 1:1 and 1 2:1 of MP5,1 . Or just backsliding back to 8 DIMM slots and leveraging higher single DIMMs to reach new relatively higher cap, but less than max of other systems. )
Apple probably won't promote 4TB because M-series is going to be no where even remotely close to that. If they stick with soldered on SoC memory modules , then probably caps out at 512GB or so. If W-3300 models tops out at 2-3TB that is still many multiples over where the "half sized" Mac Pro will peak out at.
One more thing.. I'm guessing the refreshed Mac Pro will come with an exclusive option of the mystically absent W6900X Duo, and support for next-gen & highest-end AMD Radeon RX 7000 series GPUs. Something to be very excited about.
IMHO the DUO W6900X is highly unlikely to ever ship. The 6800 DUO has more performance over the 6900 on workloads that scale in both core and/or VRAM memory utilization and and is $1000 cheaper to boot. It has significantly better $/Performance. By pricing the single 6900 at $1000
higher , they painted themselves into a corner. Doubling the 6900 price point isn't gong to be competitive. Apple OCD probably will hold that to a doubling in price ( high but highly consistent pricing model policy ).
Apple probably has some availability problem with the 6900. They are priced to reduce demand while adding a hefty contribution to the Apple "Scrooge McDuck" money pit. Apple is probably taking some of the potential 6900 Duo profits via the singles at the inflated price. Some users are going to have software which paints them into the corner of "have to" buy the 6900.
As for next gen RX 7000 support for macOS intel. If Apple keeps AMD GPUs completely frozen out of M-series systems I wouldn't hold my breath on those coming. Even more so if Apple releases a "half sized" Mac Pro on M-series that slices off most of the bottom half of what is left over of the Mac Pro userbase.
The more RX 7000 (and higher) series GPUs look to leverage the x16 PCI-e v4+ connection for shared memory traffic the more deployments into x4 Thunderbolt external enclosures are going to be more limited. If Apple is cutting down the number of Mac Pro AMD can deploy to also then at some point the relationship is quite likely to crumble.
If the relationship is already on choppy waters that too is probably another contributor to the 6900 odd ball pricing.
So I believe MacPro7,1 will depreciate a little faster as the refreshed Mac Pro will be quite interesting, definitely not boring. I guess this is good news for a lot of people on this sub-forum as most seem to be tinkerers who do not need the horse power of a latest & highest-end Mac Pro.
If Apple holds to their current path of "no dGPUs on M-series" then MP7,1 systems probably won't crater in pricing anytime soon. Many of the folks who jumped from. 5,1 to 7,1 probably won't like the "half sized" Mac Pro that Apple is going to pitch. There probably won't be a wholesale stampede off 7,1. However, folks who stretched budgets to buy the 7,1 aren't going to rush off either.
Most likely the 8,1 is being more targeted at the MP 2008-2013. hold outs who still haven't moved. And a few of the iMac Pro folks in their upgrade zone who weren't particularly happy with the iMac Pro limitations.
The overall number of 8,1 sold will probably be lower than the number of. 7,1 sold when compare the two lifecycle sales over two years . The 8,1 may sell more if Apple goes back into "Rip van Winkle" mode and just doesn't retire it for more than several years. Especially, if Apple comes in with an incrementally more affordable "half sized" model to take a deep slice of the "Mac Pro userbase".