For gaming both would be fine. You probably wouldn't notice any difference from a gaming standpoint. The choice of video card will make the bigger difference with most modern games, but you already have that picked out. IB offers a PCIe 3.0 controller, but no video card on the market even uses the full bandwidth of 8 lanes (x8) of PCIe 2.0. I'm guessing we're about 3 years out with necessarily having to move to a PCIe 3.0 solution to maintain acceptable gaming performance.
The real hype with IB is the improved integrated video and better encoding functionality. But as gamers, since this integrated video capability seems to still be in its infancy from a performance standpoint, we don't even consider using it.
As a result, I would recommend the 2500K.
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I'd also look for better prices on the 2500K after the IB processors have been out a few weeks. On the other hand, if you live by a microcenter you can pick one up for $179 now.