......This card is competing with the 7970 Ghz Edition, which uses the XT2 chip, rather than the 7970 (vanilla version) which uses the XT chip. The XT2 is binned to run at higher frequencies while also running at lower voltages. Source
This is showing an average of at least 9% performance improvement over its same priced competitor, the 7970 Ghz Edition
Also, the average price of the 7970Ghz is around $450. And if the rumors of the $400-450 price range for the GTX 770 are true, this is going to be a better performing card for the money than the HD 7970 Ghz edition.
TL;DR: 7970Ghz Edition = XT2 chip, 7970 = XT chip. Different chips. GTX 770 competes with the Ghz Edition, not the vanilla edition.