I'm loving my 760 SLI, but I don't think you'd ever need more than 2GB unless and even if you tri-SLI. Check [H]'s 2x670 4GB real world review and see that in no playable scenario was 2GB exceeded. "To really show off the advantage of 4GB of RAM on GeForce GTX 670 based video cards, would be to use no less than a three-card 3-way SLI setup." This is especially true with techniques like FXAA being developed that use less memory. 4GB cards will likely cost more and they might even not overclock as well depending.
The 770, on the other hand, can definitely make use of that extra memory if you later decide to SLI it. It's a fantastic card at its price...I would have gone that way if I had the PSU and cooling to handle it. The 770 should be available for a year, so that is part of your consideration. The 780 is just too price-heavy for me to suggest it...yes, no need dealing with SLI, but I still think dual 760s (2GB) or 770s (4GB) is a better bargain, and a single 770 will get you by for now.
Edited by NewMaxx - 6/30/13 at 5:25pm