wow I would need a different bike to do 20mph :-) I max out the gears around 16mph and my legs are pumping like mad :-) I have the torque for 20mph (if the bike can take it with higher gears I am over 400 pounds) but no where near the stamina for 5 hours. wow.
that is am impressive goal. I will always be a clyde. I don't think its physically possible for me to be under 200 pounds. I think its going to be genuinely hard for me to get to my goal of 225 and fear I will end up around 250. (there are some activities where you need to be 225 or less to do)
good luck dude and keep us informed !!