Increasing voltage would certainly help the OC of the gpu core, but you'd have to either buy an aftermarket cooler like an HR-03 (that's what I'm using), or crank the stock fan to 100% and deal with the noise. Anyway, the core clocks make a much bigger difference in performance than memory clocks, so if you can't OC the memory, it's not a deal breaker, even at stock clocks the card has enough power to put all 512mb to good use, and some games like Stalker or Oblivion w/texture mods will use up all that memory even at moderate resolutions like 1280x1024.