I dunno, all I can say form my experiance is that in one PC Ive got it has dual ATI 1900's in crossfire, and if I take one out I dont see any difference at all in maya, only if I really really up the poly count does it make a difference, textures are displayed the same etc etc

When it comes to rendering the scene ive got to say that the graphics card does nothing (if your using mental ray/software, as using hardware its the only thing that does it but how many times do you use that?) so the ram's really usefull. Ive created a character with hair and that crashes out with 2 gigs of ram with the output window saying that mental ray cant allocate enough memory, with 4 gigs it renders no probs.

As I dont play games I probably would go with the RAM and a lower priced card.