Though I agree with Next on the SLI, I would differ on the gforce Vs Quadro and Radion Vs Fire.

Ive used many Gforce and radion cards with Maya and not had a problem at all with them (as well as quadro cards), granted they are not autodesk qualified but they do work, and for the price differnce well worth looking into, if its going to be a gaming machine as well as GFX.

If you look on other discussion forums then you will find info on the differnt cards and their associated problems