All I can say it that if you've really ridden the cobbles in the Euro classics, then I am in awe.

Folks, this guy knows of what he speaks. I was an amature triathlete and avid recreational cyclist for many years. Covering 100 miles on a road bike (on the road) is trivial if you have the fitness and form. I tried to ride 100 miles on a mountain bike once (aso on the road), and it is not an experience I ever hope to repeat. I've ridden my road bike in ice, snow, dirt, and mud, and as long as you're careful you'll have no trouble. If I were to bug out by bike I'd want a sturdy touring or cyclocross bike, not a mountain bike

As complicated as a geared bike can be, I personally would never go with a fixie - I'd never get up the hills with any amount of gear, and brakes are too important (to me) for safety. I know many that disagree.