Yes, diminishing returns-but, seems like aluminum hubs and hats will dissipate more rotor heat ? I'm about to "cryo" some rotors. "Wilwood" likes the process. "More go needs more whoa", roverman.
Or just buy some:
http://www.frozenrotors.com/
I run Crager "cryo" rotors and EBC Yellow Stuff brakes on all four corners. This is an awsome combination for street, autocross, and track.