Price/performance-wise? Certainly the new 2020 iMac has the edge. But the iMac Pro quite literally offers twice the expandability. Surely that gives it the edge (as much as an all-in-one system can have an "edge" in expandability/future-proofing).
I don’t think so. If you use or plan for lots of concurrent TB3 devices at once (multiple XDR displays*, multiple SSDs in a striped configuration), yes the iMac Pro is better. In fact, a 16” MacBook Pro is better. My only complaint (driver issues with the 5700XT aside) with my 2020 iMac is the single TB3 lane. I wish it was two like the iMac Pro.
But I'll take the newer processor, more accessible RAM, and better GPU in the highest end BTO iMac (which is what I’ve got), over the iMac Pro. I have a 2TB SSD. I have 10GbE for my NAS (and that 10GbE is the same speed as if I connected via TB3...I don’t do striped NVMe configs at their prices/capacity, I use an M2 NVMe as a cache in my NAS and am accessing an array of 4 8TB disks and 4 4TB disks) and can’t imagine NVMe drives getting cheap enough for me to want to stripe them in RAID 10 or RAID 0 to get what is in practice, an incremental speed increase (I write a lot of data with video, but data transfer speeds isn’t my blocker) over the projected life of my iMac. (Meaning I don’t anticipate 4TB and up SSDs being cheap enough to RAID 0/RAID 10 over TB3 and for me to really be able to appreciate/benefit from the increased speed). For people using something like OWC's Thunderblade (which can’t get over 2700 MB/s at least with right now), which is $4100 for a 16Tb, $2100 for an 8TB, etc., you might be better off with a Mac Pro if that kind of storage and speed is a legitimate concern.
When you look at components that will blow out the TB3 bandwidth, you’re primarily looking at displays and SSDs. I’m personally not concerned with SSDs, for the reaspjs I mentioned above. With displays, yeah, the extra bandwidth is nice but you’re also limited on the iMac Pro with the old-ass Vega 56/64, which negates some of those increased bandwidth benefits. In fact, you can’t even connect an XDR to the iMac Pro without using an eGPU (which is redundant when the Blackmagic Pro is just a Vega 56 but with a Titan Ridge controller, unlike the iMac Pro) if you want to use it at 6K and I’m not sure if you can daisy-chain two XDRs off that one eGPU or not. The iMac 2020 can drive two XDRs over DSC — doing that will almost certainly zap all the bandwidth for any of your external storage (unless you’re using 10GbE), and that sucks — but at least you can connect two 6K displays without having to buy an eGPU.
If the argument is that in 5 years you could
maybe use a slightly better AMD eGPU (assuming drivers are even available in macOS, something that is not even remotely guaranteed and that I would bet money won’t happen) than the 5700XT so that you can connect multiple high-resolution displays at the same time AND a striped SSD config, fine. But that seems like a highly rare and unlikely upgrade scenario, especially when you’re looking at spending MORE money at the outset.
People with those concerns are much better getting a Mac Pro since Intel Macs are a dead-end for all of us anyway.
The better colorway, the better cooling (though I personally find the cooling improvements marginal, YMMV), and the four TB3 ports are advantages for sure — but it doesn’t change the fundamental problem which is that it is a 3 year old machine using an older generation GPU architecture, the last-gen Xeon architecture, difficult to upgrade RAM, and an inflated price point. If you can get a good deal on an iMac Pro, more power to you — that’s where there’s value. But anyone paying retail is making a mistake IMHO. You’d be better off getting a 2020 iMac, a 16” MacBook Pro or a 2019 Mac Pro, depending on your needs/budget.
* The older TB3 controller in the iMac Pro (in addition to its older and aged GPUs) is a real bummer for anyone who would want to connect multiple 5K or 6K displays (or a 6K display at all).
