Kind of a continuation of my previous thread, but I thought I'd share my progress.
I got the EVGA GTX 760 FTW 4GB, which works great when setting GraphicsEnabler=No. I also got the Dell UP2414Q – gorgeous monitor, by the way – and I now have native 4K output. But only at 30Hz. Which feels really laggy.
Windows can run the display at 60Hz at native 3840x2160 over DisplayPort 1.2, but OS X can't. I've got a feeling it's a driver problem.
I'm probably the only one on this forum with this issue, but is there any way to force OS X to refresh this display at 60Hz when running at 4K? Or do I just have to wait for new drivers from Apple?
EDIT: See my update about 10.9.3.
EDITED EDIT: See my update about the final version of 10.9.3.
FINAL EDIT: See my update after extensive testing. (My setup doesn't work, but there are other 4K monitors which do for other people.)