IMHO, disc desirablilty is, in addition to weather and hill grade, directly related to load weight. I had never had a problem stopping with my canti's...until my first heavier-than normal loaded trip. Shook me up a bit how much distance it took to stop and made me give a long pause to thinking about potential emergency maneauvers.
I have no desire to rear-end some car that hits the brakes suddenly just after passing me on a narrow road, bridge, or in a tunnel.