Just upgraded from Sierra to High Sierra in a bid to solve this issue
https://www.tonymacx86.com/threads/december-sierra-update-caused-blank-gui-windows.243370/ without having to fully reinstall (of which, miraculously it did).
After following all of the posts here, i'm at the same end as the rest of you all, a GTX 970 with UI stutters all over the place when dragging windows (ie Chrome etc). I'm also seeing slight stutters in the Water Demo.
To add to the conversation, i'm seeing the same issues on my MacBook Pro Mid 2012 Retina with GTX 650M. The UI is certainly smoother under integrated graphics (which I would use if I didn't have external screens I want to plug in), but the same cannot be said with the water demo, which runs painfully slow (I expect the iGFX is just not cut up for it).
I'm glad that I found this thread today, I just assumed it was my laptop reaching it's end of nice service, but maybe I might move back to Sierra if fixed don't come before I find the time to do so.
Hackintosh Specs: i7-4770K, 32GB 2133MHz, GTX 970 4GB, Web Drivers .106
MacBook Specs: Mid 2012 Retina (1st Gen), i7-3720QM, 16GB 1600MHz, GTX 650M, Web Drivers .106