Since I am not a qualified hardware guy, instead of guessing and possibly telling you to break something, hehe, I point you in this direction:

For a HUGE encompassing overview of how to tweak the heck out of your scene as much as possible to help rendertimes, the WHOLE chapter in the Maya HELP called Quality, render speed, diagnostics rocks!

BUT, for just pure power increases, I believe you may be looking for this page:

From the main Help navigation go to:
Using Maya > Rendering and Render Setup > Rendering > Quality, render speed, diagnostics > Increase Render Speed > Increase overall rendering speed

Good luck!