Even if the HD 7770 is OC'd it would only make it at tops 20 to 25% more but still fall short of the GTX 560 ti. I have linked you to some of the charts that will show you the difference in the OC 7770 and the 560 ti. Good luck to you.
The GeForce GTX 560 is a small bit (about 13%) faster with regards to anisotropic filtering than the Radeon HD 7770. (explain)
GeForce GTX 560 45360 Mtexels/sec
Radeon HD 7770 40000 Mtexels/sec
Difference: 5360 (13%)
The GeForce GTX 560 is quite a bit (about 62%) better at FSAA than the Radeon HD 7770, and also will be capable of handling higher screen resolutions without losing too much performance. (explain)
GeForce GTX 560 25920 Mpixels/sec
Radeon HD 7770 16000 Mpixels/sec
Difference: 9920 (62%)
Please note that the above 'benchmarks' are all just theoretical - the results were calculated based on the card's specifications, and real-world performance may (and probably will) vary at least a bit.
agreed, 560Ti best option. i HAVE owned a 550Ti PNY 1GB GDDR5 graphics card before, and i must say the xfx hd 7770 black/core edition is def slightly better then my old 550Ti of course depending on WHICH games you run.