as someone who has a 4k monitor and a single gtx 780 I can say that it depends on the game. the games I can run in 4k resolution with decent frame rate are assetto corsa, just cause 2. diablo 3, next car game. but there not all that demanding games. but even crisis 3 I can run at above 30fps if I turn shadows I think it is down. so it does work good as a single card but I am yet to try out more demanding games like last light and bf4