The K series has a unlocked processor .
If you want to OC, and use a separate video card, go for the i7-2600K. The price difference between the two is small, the feature differences between the two are few, but could be significant to you, so check the specs:
The mother board you choose is important when over-clocking. Some "play by the rules" (Intel's) regarding how OCing with the Turbo multipliers work, and others let you set multipliers sky high, until you blue screen. The ones following the rules will also limit the time high Turbo over-clocks will be sustained, while the other just let them run. OCing by changing BCLK is not how it's done with these CPUs, leave that alone since you can't change it much anyway, the multipliers are the only way, but work fine.