Even the Ghz edition isn't a huge step up from 560ti sli? I still like the less heat and power that was 2 of my reasons going single card.
It's really more of a side grade as far as FPS. If you overclock the 7970 it should end up ahead. You can chase.down some benches I'm sure. HOWEVER there are certainly good reasons too. It should be smoother. More memory and memory bandwidth. More future proof. And with crysis 3 and bioshock infinity free(if you want them), plus what you can get for selling the 560Tis, the cost about balances out. You might even come out ahead depending on the model. I wouldn't hesitate.