If i were an Nvidia guy, id be able to help...But Im an ATI guy, and the best driver suite for ATI is Omega...It makes a pretty noticeable difference in my FPS. If there's something out there for your card, grab it up! And to be completely honest with you, I have never seriously seen any kind of ultra significant increase in my video performance from OC'ing a video card. I have seen higher scores on like 3d Mark, but they havent ever been anything higher than a couple hundred points. OC'ing your bus tends to help too, thats usually a bottleneck.
Good Luck!