I rode MTB's for years prior to switching to road but, I really didn't do much tech stuff, downhill or singletrack. I've ridden four RTA BigRides which are run mostly on sealed bitumen and dirt roads, on a C_dale rigid. This and my road fitness would maybe help some with endurance but I would probably be walking difficult downhill sections. I'm looking at it more as a social fun ride, not a race in any way at all and I have no qualms about quitting if it gets too tough.