It would be interesting to see the pad surface area/torque moment on a disc vs. the shoe friction area/torque moment on a drum. What is nice about a drum is that the shoes are pulled off of the drum, reducing drag when the brakes are not applied.

I don't think that enough braking on a 2G is done in the rear to really cause concern for heat. This definately holds true once the fronts are upgraded. The more effective your front brakes/tires are, the less effective your rear brakes need to be.