Well, finally decided to return mine after messing with it just a little longer; it's going back to the egg first thing in the morning. I'm really sorry if I steered anyone wrong on these - it just seemed like a good buy and was always my dream card.
For what it's worth, I have a Gigabyte 5870 @900 that does Moo! WUs in 26 and some change all the way up to 29mins, depending on what else I'm doing on the computer at the same time. Also (2) GTX 460s in there crunching DiRT, and all 6 CPU cores crunching DiRT - I am not holding any back while DiRT has CPU WUs, so that could be upping my times a little bit.
@SteVe - what is your mem clock speed on that 5870 that's doing them in 26mins?