[Goku]

Nearly every review out there has a overclocking portion covered if its a K part Intel CPU. I suggest looking those up and see how the games you currently play react. Overclocking performance gains depend entirely on the game. Its not linear scaling. The 2500K is cheap on Newegg right now. Costs the same as a non K IB part at the moment. Far better buy.

Well don't order anything off that build just yet. What exactly are you tweaking? Please post it here to avoid getting something unnecessary. There is new deals out there so I would probably change a few parts in that right now. Just let me know when you actually want to order this.

You can put either Nvidia or AMD cards with Intel. What you want entirely depends on how much money you can spend. If you are still curious check out some reviews to see how the current gen performs.