HardOCP recently posed this comparison showing performance between the 7870, 660ti, 7950, 670, 680 and 7970 using the latest drivers (NVIDIA Beta and Catalyst 12.11).
Results are pretty interesting. AMDs new drivers really give the cards a pretty significant performance boost.
ANYWAY, if you're beating your head against a wall trying to pick you new GPU, here's a link to the article:
http://www.hardocp.com/article/2012/11/12/fall_2012_gpu_driver_comparison_roundup