K-Oicks :
a pair of 470's will beat a pair of 560 ti's?
sorry I don't know that much about video cards so this may sound stupid.
EDIT: if it matters my motherboard is ASUS P8P67 Pro and I'm running on one 27" monitor
a Single 560 beats a single 470 by a bit, but in SLI the 470s scale better than the 560s... Which means in SLI they are about the same.
The SLIed 470s have a greater power draw than the SLIed 560s. Meaning you need a bigger power supply.
The SLIed 470s have more memory than the 560s which means that at higher resolutions the 470s will outperform the 560s
If your 27 inch monitor is 2560 x 1280 the 470s would perform better. If you have a 1920 x 1080 monitor performance is a draw so I'd go with the 560s to save on the power bill.