It isnt? I use 2.4-6GB at 1440p Ultra...You COULD always get a GTX 780 (3GB) now, and one later. I had originally thought that newer games (like BF4) needed a min of 3GB VRAM at 1440p, but that does not seem to be the case.
Also, +1 for a single card over two out of the gate. 780/780ti, AMD 290/290x are the go to cards at this time for that resolution IMO.