So, I think it is more apples to apples than you think. I wish the car I used to track was 2k lbs! that would be awesome. I was making the comparison of my 4Runner going down a windy two lane road at 40-45 mph slowing repeatedly for curves is very much like my 3500 lb stock sedan lapping a race track. In fact I would say the energy dissipated slowing the car on track is a greater demand on its braking system given the triple digit speeds and what not than the 4Runner on Old Priest grade, even though it weighs 1000 lbs more.
It is good to know though that the stock system works well enough to survive the conditions you put it through and mentioned above. The whole point of my original post was to find out if the TRD pads have a higher operating range than the stock ones seeing I reached the top end of the original pads pretty easily. All be it only once in the 8k miles I have driven my 4Runner.