We've climbed & descended most every paved mountain pass in the Colorado Rockies. Also climbed & descended Mt Evans & Mt Haleakala on Maui - all with rim brakes. Never had an issue. On a couple of occasions I became concerned that the rims might overheat (steep, winding road, hot day) and stopped to check the rims. They were hot but I don't think we were close to a blowout. While this is just our experience, there is no way to compare how this might have gone with disc brakes. I don't know if any of the teams out there have a more apples-to-apples comparison.