Francisco Costa :
Right now the GTX 780 ti is the only card that will get you playable frames at about any game in 4k resolution
Not true the 780ti cannot even max out all games @ 1440p, you will need SLI 780TI or even better crossfire 290 or 290x's.
The better solution is Crossfire 290s the larger bus and extra vram make a difference, the 780TI runs out of buffer in games like FarCry 3 @ 4K