Over clocking that card might net you 61-71 fps if you are already getting 60-70fps. Your best bet is to save up for a better card.
That doesn't seem right. At the lowest clock speeds (300 core, 500ish mem), I get about 30 fps in the benchmark built into Afterburner, but at stock speeds (570 core, 999mem) I get around 60fps. If my math is correct, I should see at least a 15-20 percent increase in performance if I overclock to around 670 core, and 1200 mem.