I'd suggest the GTX 570, it'll destroy the 7770 in performance. Although the 7770 would use less energy but they just don't match in performance.
I have a 680w PSU, so power isn't a huge concern, just buying older and used hardware is what kills me.
How much of a bottleneck do you think I would have with the 570 compared to the 7770?
My only problem would be if the $50 extra I put down on a 570 really wouldn't show better performance because of the bottleneck from my Q9400. I heard if you overclock it from 2.6Ghz to upwards of 3 Ghz it might help but my CPU Cooler is a piece of trash.