The 560Ti will be faster, but if you don't want to spend the extra dough, then I would get either a 6870 or regular GTX560. At this point, it is whether or not you like either Nvidia or ATI.
------------------------------2500K @4.2| 212+| MSI Z68MA-G45| HIS Radeon 6950 2GB UNLOCKED TO 6970| 12GB Corsair RAM| Ultra LSP 750W| NZXT Vulcan| AOC 23" Reply to Deemo13