Overclocking your graphics card can improve its performance by 5% to as much as 15% (or more), depending on the particular card model. Of course, as with any overclocking, care should be taken to ...
IIRC, the OEMs were clocked at 90 MHz and the retails were clocked at 105 MHz. I had a retail one a few years ago and can't remember what I ran it at. Maybe 115 MHz, I dunno.