The 560 Ti will annihilate the 7770. It's a much better choice. The 7770 is efficient, but that is about the only thing it has going for it. It's not cheap, and it's not fast. There are a few deals for 560 Tis that bring them below $200 post-rebate, too.
Comparison of benchmarks: http://www.anandtech.com/bench/Product/536?vs=547