Yes, you will be gpu limited. I have GTX 560 ti in SLI and am almost always gpu limited (CPU is i7 920 at 4GHz.) CPU is very rarely a limiting factor in current gains if you have a fast processor like yours (and mine).
The performance gain of an overclocked 2500k vs an overclocked i7 975 is not that great even in CPU limited situations such as video editing. In games you won't see any benefit at all.
Btw there's one quite popular fallacy doing the rounds. People know that the CPU and the gpu are important determinants of performance in games. But they take it a step further by thinking that if they have the most modern generation of gpu, then they must also have the most up to date CPU. Not true at all.
If it were my money I'd leave the CPU and mobo alone and spend what you save on a faster gpu configuration. This could be either 2*6970s or the recently launched 7970.