I havent tried the 9700, but I have compared the 8800 and the XGL750 on the same dual p4 2.2 gig win2k box and the 750 was the better performer in maya. The 8800 was prone to crashes or freeze ups with render-view and hypershade running. The 750 is pretty stable, but still has some gl issues - visor icons not showing up sometimes, hypershade text not visible etc. Restarting maya fixes these though.
One little trick i noticed helps the "sub pro" cards from exhibiting the glitches in the visor/hypershade/ect like David mentioned is to NEVER close down a window when you open it. Minimize it instead when you don't need it and they should still work funcitonal with the text and all. On my pc's it seems like it only starts getting glitchy when I close down a window and open it up later.