Almost every review overstates the graphics card requirements necessary to play games at 4K resolution *with g-sync* enabled.
I've had this Acer XB280HK monitor almost since the day it came out. For the first several months I used it with my old GTX670. At 4K. No problem. It was awesome.
Now, I'm not a FPS player, and I do tend to play games that are a year or two old. But for games like the latest XCOM, Total War, and many others.....it did just fine. At 4K.
Eventually I upgraded to a GTX980 because......well, why wouldn't you? It's cheap, fast, and doesn't draw allot of power. Also.....it let's me play Dragon Age...at nearly maximum quality settings.....at 4K.
So, don't be scared away from this monitor because you think you need a thousand dollar graphics card.
It's not like game developers are CREATING games with 4K levels of detail....yet.