I avoid 100 mile circles at all costs.

I have biked 150 miles in one day on a loaded touring bike weighing better than 70 lbs on some roller-coaster hills and flats with no problems wearing ATB shoes, although I understand the theory behind roadie shoes. During an actual race, or a century where you are trying to git-er-done in a reasonable time, you would probably be hunkering down on those pedals a lot harder than I.