I read that with that high resolution its best to go with the 4gb version, is that correct? Also, would the upgrade to 680 not be worth it?
NO! It is common knowledge that the 7970 GHz is far stronger than the 670, and the gap only widens at high resolutions,
Also the 4GB version is a complete waste. After 2GB, the 670/680 bottleneck because of there bus size (256 instead of AMD's 384).