Ah, I'm so glad I saw this thread! I just did this and bought the Zotac GTX570 from Microcenter, I love it and it's over clocking alright. The biggest problem right now is one that easily amendable... I need a more powerful PSU greater than 550watt. OCing shuts the computer down because this card is drawing more power than the PSU can deliver.
I also think (but don't quote me on this) that the gtx570 is the optimized version of the gtx480. Correct me if wrong please.