I've been racing on 2WD rear discs and calipers and the rear pads have been wearing away very quickly because of the heat. Now switched to 4WD set up at the back with vented discs and see less pad wear and presumably cooler rear brakes. I couldn't say that I've noticed much improvement in braking though.

Pics here if you're interested: http://racecarprep.blogspot.com/2009...and-discs.html

Charlie