Found some benchmarks of MSI TwinFrozr III HD7950 OC
vs. MSI Power Edition GTX670 OC
OCed HD7950 easily keeps up with the OCed 670. This makes it a very good deal and especially so for just $20 more over 660Ti.
MSI TwinFrozr III 7950 @ 1167mhz
MSI Power Edition GTX670 @ 1300mhz
MSI GTX670 Power Edition is $413
with shipping on Newegg, or almost $100 more expensive