Right now I'm using a 256mb 6600gt as my main video card. I'm considering upgrading it, and  I was wondering; what effect will that have on my Carrara performance?  I'm thinking it would have to do with my opengl handling speed, am I correct?  What should I be looking out for (amount of on-board memory, clock speed, etc...)?

Also, during renders, is my video card used?  The reason I'm wondering is that I'm considering a passive card and don't like the idea of a renderer using it at full-speed and therefore heating up my system.............