Hey,
As said, the extra Video Memory is pointless if a game doesn't use it and there really are NO games that would use more than 2GB with a GTX770. I could give a handful of scenarios where you could use more than 2GB with a GTX770 but every one of them would make more sense to drop the anti-aliasing, or use lower quality MODS to keep the frame rate high enough and then you'd be below 2GB again so the 4GB would give no benefit.
The only logical place to use a GTX770 4GB card is in SLI with two or three cards with a very demanding game and/or 2560x1440+ resolution.
You should be looking at one of the following assuming your CPU won't bottleneck too much (i5-2500K/i5-3570 or similar).
a) Asus GTX770 2GB ($320 USD), or
b) EVGA GTX780 3GB (967MHz ACX cooler). $510 USD.