I have melted a pair of brake pads to the rim on a long steep twisty downhill on a blistering hot day (from 5000' to sea level in 5 miles). I replaced them at the bottom. Took 10 minutes. The days of blowing tires off the rim from heat are long gone with the advent of hooked rims. Oh, I suppose you could do it if you really tried, but it's also fairly easy to allow the wind to help with braking by sitting up, and pulsing the brakes to let the rim cool.

My ultimate touring grouppo is one that's easy to work on, ubiquitous and rugged. Suntour power-ratchet bar-end shifters, Deore LX derailleurs, 7 or 8-speed cassette, Deore LX hubs, Mavic A719 rims, Alpine spokes, canti brakes, Sugino XD600 crank. (OK, the canti brakes are just a nod to retro-grouchhood. Vee's would be fine too).