Well they are both great cards but to answer your question the GTX 670 will perform better in your preferred game-types (BF3, GTA IV, open world games like Skyrim and Fallout 3). It's also cheaper than 7970, and allows gaming with PhysX and Adaptive VSync.
http://hardocp.com/article/2012/04/16/nvidia_adaptive_vsync_technology_review/
http://www.techpowerup.com/reviews/AMD/HD_7970_GHz_Edition/27.html TechPoweUp gives the 7970 Ghz Edition an 8.5 rating
http://www.techpowerup.com/reviews/AMD/HD_7970_GHz_Edition/33.html
TechPoweUp gives the MSI GTX 670 Power Edition Twin Frozr IV an 9.7 rating http://www.techpowerup.com/reviews/MSI/GTX_670_Power_Edition/
Quote :MSI's GTX 670 Power Edition uses the famous Twin Frozr IV cooler from the MSI Lightning and comes with a large clock speed boost out of the box, making its default clock speed even higher than GTX 680 stock clocks. MSI is asking a $30 price premium for their card, which doesn't look unreasonable, given the improved cooling and higher clocks.TechPoweUp gives the 670 TOP an 10.0 rating, the only 10.0 rating ever
http://www.techpowerup.com/reviews/ASUS/GeForce_GTX_670_Direct_Cu_II/33.html
Quote :
Overall the ASUS GTX 670 Direct CU II is the best card I ever tested.I simply can't find anything wrong with it.