The 560 isn't enough a jump over the 460, particularly the Superclocked model by evga (I've the same card). If you are going to upgrade to a single card solution, you'd only really find value in a 570/6950-level, and that is only at 1920x1080 or higher resolutions. And given how close we are to the 7xxx series, if you wait you can get either a better deal on this gen, or score a solid single-card solution.
16-55/28, 56/1.2, 18-135, 55-200
Minolta MC 50/1.4, MD 35-70/3.5, 300/4.5 and a bunch more.