First, I commend you for spelling "brakes" correctly (do a search on "breaks" sometime!).
Any real upgrade would involve increasing the mass of your rotors. No mass change equals no upgrade. Simply changing calipers will not increase how many times you can stop before the brakes overheat.
Do a search on "brakes" and check out Bill Verburgs excellent treatise on the subject.
http://home.nycap.rr.com/wmv/generalbrmd.htm
-Chris