for gaming i recommend to go with 2500k, it doesn't matter if 2500k doesn't support PCIe 3.0, you can put any PCIe 3.0 card into PCIe 2.0, you'll get about similar performance of PCIe 3.0.
Pcie 3.0 is backward compatible to pcie 2.0 which means there is absolutely no change in performance.
After building a 3570K on the weekend I wouldn't recommend it for value for money or being future proof ... and buying that K for overclocking in an IVB processor is just a scam Intel should be held accountable for.
Whilst K means something with the SB processor it means NOTHING for an IVB processor past being able to move the multiplier up ... what happens next is a dissappointment.
The stock cooler is ok but it gets hot after a decent gaming session and forget overclocking it beyond 4.2Ghz with any reliability unless you get a honking great cooler ... then thermally it chews more power as it ramps than SB. ... negating the whole reason for buying it.
I'd recommend an i5-2500k.
The PCIE 2 vs 3 is a fizzer of a reason to buy something now anyway ... bit like all of the hype bewteen SATA 2 and 3.
Buy what works now.
IVB is a mobile processor ... the desktop variant is rubbish for a gamer.
Sure 4% better IPC ... but it heats up under load and won't overclock.
With the poor TIM under the IHS these will be dying in droves as people melt them over the next couple of years.
Just my 2 cents worth.
K stands for Kill it quick on these ... electromigration.