Is there something else you can OC? In times of old there were some cards that could have things unlocked, but none of the recent cards that I know of are like this. You can OC the core, shaders if possible, and the memory frequencies. There isn't really anything else to OC.
From reading the OC part of reviews, if you can bump the core and memory up, it will only be a few %. The frame rate will raise the same or some depending on what was limiting it before. So 2% on the core and 4% on the memory might raise your frame rate anywhere between that. A 4% increase? Not worth the increase in voltage, temps, stress on the card if you ask me.
Hey, haven't you heard? Its time for a new avatar.
Actually OCing your card can benefit a great deal. Of course it depends on the card. For instance my 5850 has the standard clocks of 725/1000, when I OC'd it untill 1000/1200 you could see it reached the performance of the 5870.