770 2gb > than 760 4gb and cost the same. 770 eats high/ultra settings most of the time, 760 needs the settings a good amount lower to be smooth, I've seen both in action.
Save your money and grab the 2GB model. It's more likely that you will come across a game that is simply too demanding for the GPU than a game that requires more than 2GB, even at resolutions higher than 1080p.
770 2gb > than 760 4gb and cost the same. 770 eats high/ultra settings most of the time, 760 needs the settings a good amount lower to be smooth, I've seen both in action.