Hello. I've enjoyed reading this thread. Everyone seems to be very helpful with regard to the question posed. I've never entered a 100-mile biking event, but I have participated in many rides longer than 100 miles. One of my problems on long HOT bike rides is staying hydrated and not falling pray to heat stroke. Once the heat gets the best of me, it's really difficult to continue. And rest out of the sun is really the only way to recover. You cannot just drink a lot and cool down. This issue seems to have been ignored in this thread.
My advice for long hot rides is that you must be very regular and timely on ingesting liquids. Also, you must be knowledgeable about electrolytes (salt, etc) so your body can use the hydration that you are ingesting. Salt tablets (sea salt) are good. But if you find yourself at at a rest stop on the ride and you forgot your salt (or ran out of it), then consider getting a bag of potato chips sprinkled with sea salt. If you don't stay hydrated during a very hot ride you are destined for failure. This holds true regardless of your fitness level and preparation for the ride. Good luck!