Whoooa, let's take a step back. We assume that you're talking gaming performance, but the question we need to ask is: which games are you looking to play? The 2500k can be overclocked to remove almost all functional CPU bottlenecking from any game when using a GTX 680. But not all games are created equal; if you're wondering about AvP, then you could underclock the 2500k to 2.0 GHz and still push frame prerenders to 2x GTX 680 with no bottleneck. If you're playing Crysis 2, then you'll need to overclock the 2500k a good bit to remove the functional bottleneck. I have done extensive testing with a 2500k with single/SLI 460s and single/CF 7970s to corroborate what I have said.
Given all of that, the 2500k is obviously a great performer at stock and you shouldn't have too much problem even if you weren't to overclock (though I see no reason not to, you can do it even with the stock HSF and 30 seconds of Interwebs research) Did you have any questions about specific games and framerates?