I know the my 560ti is about on par with the GTX 570, slightly worse...but both cards get beat by the 660ti quite easily. then theres the GTX 580, which performs about the same as the 660ti, but more power hungry and just less efficient.
I know the 7950 is the best deal, but I prefer Nvidia. Don't ask me, I just do lol.
Or should I save up for something like a GTX 670~690?
This is Toms' Hardware graphics chart. Note they say not to upgrade unless it is at least three steps higher. For your 560TI, that would be a 670. The 560 or 660ti are only two steps up, not enough to be worthwhile. Of course, you could go four steps up to a 680. Right now the sweet spot for Nvidia is the 670, 95% of the 680 at about 70% of the price. I'd go with the: