I'm on the ATI Radeon x800 at work and haven't had any problems so far (on 6.5). The new Radeon x850 XT is a build to order feature at the Apple store, might wanna look into that. Was getting good reviews on PC sites.
I kind of had my eyes on the 850XT on the apple website, but I wasnt sure if it would work well or not with Maya. I am gonna search for some of those magazine reviews to see what the card can do, but its great to hear some input from someone that is actually running it on a daily basis. Thanks a lot for the reply.