These Macs unfortunately are approaching 9-12 years of age (considering the 2009 4,1 machines that got upgraded and flashed to 5,1s). They use some older standards with PCIe v2, DDR3 memory and older CPUs that lack some of the features of modern CPUs. At some point eventually it will make sense to upgrade these tanks of a Mac, but what if you like dual booting (MacOS when you want to be productive and Windows 10 when you want to get the most out of your gaming options)? That leaves those shiny new M1 Macs out of the picture. What if you don’t want to deal with the T2 chip and the pitfalls that come with that mess (not getting into the full debate on that – that’s a whole topic of its own)?? That leaves the iMac Pro out, along with the 2018 Mini, 2019 Mac Pro, 2019 MacBook Pro and generally all Macs made 2018 and later.
Aside from going the Hackintosh route, I found one great option and good news… prices trend around $2000 gently used and even new, it avoids the horrible T2 chip while still getting great overall performance, has excellent onboard graphics options for Metal, has native Thunderbolt 3 and reasonably fast PCIe v3 speeds externally. RAM/Storage are socketed and upgradeable and even CPU upgrades are possible (thanks to being a socketed LGA 1151 system).
*Drumroll* Enter the 2017 27” Retina 5K iMac with 8 GB Radeon Pro 580 and 4.2 GHz i7 7700. Looking long-term, you may truly be able to squeeze more out of this machine than the aging Mac Pro 5,1. Single core scores are almost double the X5680 3.33 GHz and X5690 3.46 GHz Xeons in the 5,1 (single core scores are a big deal since most applications and games are STILL single threaded). Prices are less than 1/2 the iMac Pro base (which also has a T2).
While you are a bit choked on eGPU bandwidth with that single PCIe 4x path on DMI3 at 8 GT/s per lane (or a max throughput of 32 Gb/s), that’s still plenty to sustain 4K 60Hz or 1440p 120Hz video connections while having enough leftover to not compete too terribly with your NVMe storage.
Overall, the 2017 27” Retina 5K iMac may be the best bang for your buck right now while avoiding the T2 and maintaining a level of compatibility with x86 derived code. If you go with a unit equipped with the Radeon Pro 580 8 GB, it’s going to be good enough for VR and 1080p/1440p gaming out of the box, handle 4K video rendering nicely and will be great for general use overall while being fully natively supported under the current OS (likely for a few more years to come too).
The only real downside with these iMacs is that DMI3 didn’t evolve to a full x16 or even an 8x path to give more breathing room to eGPU and storage, but even at the paltry 4x overall external bandwidth at PCIe v3 it’s enough to get by and have adequate future expansion options without dealing with the T2 while having plenty of internal upgrades available at your disposal.
I may wind up considering this machine myself if I move away from my Mac Pro 5,1 at some point down the road. It’s a great overall value for what you get and is among the last and best expandable Intel Macs made without the T2 chip.