For reference, when comparing to newer GPU charts/reviews, two good 560Tis in SLI is about the same
as a 670, while two oc'd versions is equivalent to a 680.
Your CPU could easily be a bottleneck, but it depends on the game, resolution, etc.
Unless you're in a terrible hurry, wait for the Maxwell launch, see what happens to pricing, etc.
If you're open to used options, 7970s can be had for good prices and are decently faster than
a 560Ti (7970 is basically the same as a 280X). If you don't care about noise or power, a couple
of 3GB 580s is potent (about the same as a 780); two 7970s are faster, but I had a lot more
driver issues testing 2-way 7970 CF than even 3-way 580 SLI.
If you want to buy new though, I'd say a 4690K, decent Z97 mbd, and wait for the Maxwell
launch to see how things shift, even if it's just better pricing for older products.
Can you run various standard tests like 3DMark (Vantage/11/13), Call of Juarez, Stalker COP, etc.
I could compare to results I have already with the same card & others.
Ian.