I am now running an Acer xb280hk 4k with an Asus 970 OC, and everything works smoothly, highly recommend this set up. Steady 60 fps, in stations can drop to 38fps, aa and blur set to off (not needed), no stuttering at all even in stations, so you wouldn't know that the fps is lower there, this may be because of the G-sync. Altogether as smooth as the gtx770 it replaced.
I run the same monitor with an Asus 980 Strix (980 with a 10% factory overclock).
Solid 60 FPS outside stations and about 55 FPS inside stations. Only the steam/smoke effect in the hangar causes a slowdown to about 45FPS on occasion but it's still smooth due to GSync and... it's just the hangar lift so who cares?
I use maximum settings apart from AA which isn't needed (as above).
4k is absolutely stunning to look at. Nothing else looks as sharp and has the graphical detail to make it really work. I considered multiple monitors but there didn't seem much point with OR CV1 round the corner.
AMD? no ta, my house is warm already