The 560ti is the best performance with the 448 version being a spin off of the GTX 570 but although costing near a GTX 570 doesn't give the perfromance of a GTX 570. Sadly the GTX 560 Fermi cards have run their coarse, AMD's 6850 and 6870 are both cheaper and deliver in most cases better peformance and scale well, add to that a $220 7850 more than handsomely beats it running a GTX 570 to the limits. If you want Fermi I say look at a GTX 570, fantastic card still otherwise look at 7850 and 7870 which are priced well.
Performance probably has the edge, consider the 6970 is basically only able to compete with the 570, but the issue is pricing and the price/performance. The 560ti's were pandering around at $250 long after AMD's GCN was out while a 6850 barely cost $120 and a 6870 around $170, the 6850 competed against the 560 while the 6870 was more in the 560ti bracket with the 6950, the problem therein lies that the 560's tired architecture is overpriced and super ceded by a faster 7850 which runs as above a 560ti 448 and 570 to the limit.