100MB??????
What the crap is your machine smoking?
I understand about the animation render... what machine are you running? Also, yeah, you could use maya software render, or even hardware render, but I don't know how that would be faster then Mental Ray by far... I don't use mental ray, nor do I use IPR, and some of my scenes dont turn out horrible at all. Well, keep up the good work on your scene.

Cheers,
,Matt