GTX 770 4GB or GTX 780ti 3GB?

[JEMC]

780Ti hands down. You'll yourself without enough power to run your games with the 770 before you ran into problems because of lack of memory with the 780Ti.

Alternatively, you could go with a Titan Black and have more power than a 780Ti and also 6GB... or wait until Maxwell comes to see how fast and how much memory they have.