I think you might be wasting your time. You could overclock this card to the gills, and it will still get beaten silly by a HD6570 or GT630. If you're just doing this for practice or as an exercise, keep a close eye on temps as you gradually increase clocks and bump voltage, perhaps 0.05V at a time. If it either overheats and throttles, or becomes unstable or artifacts, and another 0.05V doesn't help stability, you know you've crossed the maximum limit for the card.