The integrated GPU in the new Mac Mini (Intel UHD 630) is, at best, mediocre. And from my understanding it is not latest gen. More info from MacRumors thread below:
https://forums.macrumors.com/threads/mac-mini-2018-intel-uhd-graphics-630-pros-and-cons.2150795/
I am myself considering purchasing the New 2018 Mini - it is either that or update my Hackintosh. I love and prefer the Mac OS, but most of my work now is done on the PC. Cheetah is the only program I rely on for the Mac (Adobe After Effects and Premier Pro in latest update even support Apple Pro Res on Windows).
The lackluster GPU on the new Mini could always be offset by using an eGPU. More problematic for me is the fact that the SSD is soldered to the motherboard and not upgradable, which means you have to shell out up front for the largest capacity you think you will need. Not to mention if there is some kind of system crash, it is impossible to simply swap boot drives. Still, a maxed out 2018 Mini with 10G fits into my current needs really well.
Regarding the Mac Pro 6.1 - I personally would never invest in such a machine as it simply offers little over my Hackintosh. The introduction of the trashcan Mac is what drove me to build a Hackintosh in the first place, as I was getting heavily into GPU rendering with Nvidia cards. Also consider Apple will unveil a newly designed Mac Pro sometime in 2019 with promises of “fixing” the mistakes they made with the trashcan Mac Pro. This of course remains to be seen; I’m not highly optimistic. I also know whatever they do come out with is going to be super expensive.
Like Swizel says, trying to find a cheese grater 2012 Mac Pro could be a feasible option. With some minor restrictions, they support OS High Sierra and even 10.14 Mojave when “equipped with a recommended Metal-capable GPU". Those older Mac Pro’s were build to last; I still on occasion use a 2008 Mac Pro!
FYI Swizel: I have been using a Hackintosh for freelance for the last 5 years. And while I did have some issues, it has been remarkably stable. I think that as long as you have a real Mac (even if older) to fall back on then the risks are minimal. To mitigate such issues while on a job, you can also use a NAS to centralize working files so that you can use the other machine to continue where you left off in the event the Hackintosh can’t boot.