I don't know if 4k is worth it. In stores which have 4k TV's I can't tell the different directly next to a 1080 tv, unless I'm so close that I can't see the whole screen, which would be like sitting at the front in the cinema!
on the other hand, my phone is 6.5" 1080 = 13" 4k screen, so a 24" 4k monitor is kind of low res LOL!
Current GPUs can't really handle 4k, even dual GPUs. It doesn't help that we are getting crappy inefficient console ports. Perhaps dual GTX880 will.
Personally, I prefer multimonitor, it's just amazing to have your horizontal FOV filled, with the lights of in the room it really immerses you into the game.