I agree with the power supply.
I suggest one like this: http://www.newegg.com/Product/Product.aspx?Item=N82E16817139011
Be sure to not get a cheap PSU. That's going to be the thing powering your system and you want it to be one of the most reliable components in there.
Also, I've dabbled about in GPU Overclocking and it's not really all that much worth it. The most I've ever gotten was a couple FPS better than what I originally had, and if you're planning on running that card in SLI with another one on a 23" monitor, then they'll destroy the games you're talking about without being tweaked in any way.