I heard there both good card for 300 dollars ehich is better.
7950 is a different class of card than the 660Ti
the 7870 competes with the 660Ti
If you can get a 7950 for the same price as a 660ti, grab the 7950, no questions asked. 660ti is probably good, but it's not 7950 good, and it's not meant to be.