I was thinking that a 670 or even a 660ti would only give me a modest frame rate increase and that it might be better to hold off for the next gen GPUs.
Looking at Bench, the 660Ti would give you an average 53.1% more performance
and the 670 would give you 74.7% more performance
than your 560Ti (all numbers for 1080p resolution). I'd say that's more than a 'modest increase'. You are right however that your CPU might be holding the GPUs back, so you may not hit the same performance increases that Anand did.
EDIT: Didn't realize that you were running a Q9550 CPU. If you're going to be doing any heavy CPU lifting, then a corei5 would be a good upgrade; the 560Ti is still a decent GPU for gaming and should last you a little while longer.
EDIT2: Guess you already came to the same conclusion. That's what I get for not reading through all the posts
Wind, Sand and Stars.