Oh, just to support 4K show like maybe when watch 4K show at youtube?
The gtx 950 to gtx 980 should be able to support 4k monitors. Youtube and watching movies should be ok. The problem is gta5 and battlefield 4. I don't think you can run them smoothly in native 4k res using those cards. Which defeats the purpose of having the 4k monitor in the first place.
I am playing on a 2.5k resolution. GTX 970 was the ideal choice.