I switched from Mac Pro to PC a few months ago. We needed NVIDIA and running some hack over thunderbolt isn't a real option, despite what the Apple Zealots say.
Recently made the same decision myself to use CUDA too. After months of considering hacked open thunderbolt enclosures that nearly cost the same as a PC anyway I just switched.
I now measure my 3D render times in seconds not double digit minutes.
There is no doubt in my mind that if the trashcan mac had Nvidia GPUs I would have just saved up and spent over double I spent on this PC even if it had worse performance. I've been a mac user for 17 years and didn't make this decision lightly.
Can I ask what sort of rendering you're doing? Do you mean animation or still images... what software? I find that between different software you can get vastly differing render times. Also, for really serious and large work aren't people using render farms now anyway?
Doing animation and still (admittedly haven't produced anything yet as I've only had this setup running for a week) mostly motion graphics and advertising focused.
I'm working in Cinema 4D and Octane render (render engine built from the ground up for GPU) with a single GTX 1080, coming from a 2.7 i5 MBP with no dedicated GPU the difference isn't even comparable.
The industry is at a bit of a crossroads from what I can see, of course huge studios have investments in render farms and CPU based tech but for individuals and <10 person studios it's all moving towards GPU rendering.
Being able to run a renderer on your desktop machine that can show the end result in near real time completely changes your workflow. It's no longer just using experience to make guesses with lighting and materials then waiting minutes to see if your hypothesis was correct.
