The two cards are pretty evenly matched: http://www.anandtech.com/bench/product/770?vs=829
For gaming at 1080p, 2GB is fine. And remember, the more VRAM the card has, the more system RAM the OS will set aside for it.
The rest of the build looks good. I don't know if the cooler you chose comes with thermal paste or not. It might be best to order some MX-4 just in case. Besides, it's always good to have on hand.