yes its a good choice. the 7770 is twice as powerful as a 6670 so your frame rates should theoretically double
Just a quick glance at the benchmarks, I'd say at least double. But I think a more difficult benchmark is being placed on the 7770, so if you're running your games with the same settings, probably more than double.
Nice choice, the 7770 is a really cost effective/powerful card. Your framerates will take a solid boost, probably double by a conservative estimate. Nice processor btw, I'm currently running the FX-8120