More pistons in theory gives you an overall larger surface area to act on the pad, and gives a more even, consistent pressure over a greater length of pad than fewer larger pistons would. It\'s analogous to storing round jars in a square box, the smaller the diameter of the jars, the more you can fit in because they tesselate better, thus storing a greater overall volume. It\'s got as much to do about the trends of the time as any real practical advantage in anything but the most competitive of race conditions, though. You could see the trend in motorbike developement recently, back in the mid 90\'s when Yamaha first put six-pots on, all the other manufacturers had to follow suit to cash in the trend. Now you can\'t find a sportsbike without the de rigeur radial-mounted four-piston calipers, and the six-pots are no regarded as old hat.
Pad compound and disc material probably have more to do with how well a brake system copes with heat transference than caliper design or the number of pistons. You want a disc that gets to operating temperature very fast for instant bite, but does not store heat beyond its optimum range, and a pad that drops heat very fast without passing too much on through the caliper to the fluid, because its when the fluid starts to get hot that the brake efficiency really takes a drop. Then there are other factors like how much moisture content has corrupted the brake fluid, how far down the pad is worn and so lost thermal efficiency, and many other variables. Simple to explain and understand, very difficult to put in to practice and maintain at optimum efficiency! :yes
nice thread resurrection, btw :Thumbs-up