I just wonder, is it possible to install Win10 on its own internal ssd on the 7,1 (means not on macOS boot ssd)?
So for gaming it would be cool to add a fast NVIDIA and use it for WIN10 on the 7,1.
Yes, entirely possible. Not quite as easy as just using the Boot Camp Assistant, which partitions the boot drive, but still doable. You basically just use another PC / virtual machine to set up the separate drive, then install Apple's Boot Camp drivers (downloaded beforehand from a menu command in Boot Camp Assistant) onto the fresh Windows 10. Make sure you disable Secure Boot in Recovery.
As a gaming PC, a Mac Pro is quite a good performer,
even with the Vega II. Although, I found in the brief tests I put it through that CPU bound games would really be better on an overclocked i7 at closer to 5GHz than the Xeon which tops out at 4,399. (IOW, not giving up my watercooled, lovingly handcrafted rig.)
So, I can't see any reason an RTX 2080Ti couldn't live in there purely for Windows 10 use. Expensive way to game, but if it's the only machine around for after work use, go for it. (I've considered trying that card in, but I like to have my GPU part of the watercooling loop and it would be very tedious swapping back and forth, even for a one time trial.)
