I think PhysX is much more than just a gimmick. Alice: Madness Returns is another game that looks absolutely beautiful with PhysX enabled. Admittedly some games don't seem to make great use of it at all (even though they advertise it), but the ones that do look incredible.
Having said that, the 7970GHz is significantly faster than a 670, especially at higher resolutions. My personal opinion is that if you game at 1080p, the difference is small enough to make PhysX support a decent trade-off. If you game at a higher res than that, the 7970GHz would probably be the better bet.
Having said that, the 7970GHz is significantly faster than a 670, especially at higher resolutions. My personal opinion is that if you game at 1080p, the difference is small enough to make PhysX support a decent trade-off. If you game at a higher res than that, the 7970GHz would probably be the better bet.