I am 6'2 280lbs. I havent fallen in love with many single speed bikes. But I have had alot of fun on hobbits, derbi, vespa, and morini mo2. that being said I have had a single speed vespa with a tuned clutch and ridden a case inducte minarelli w/ case induction and tuned clutch that were plenty capable. Any of the variated bikes mentioned above are easy to get 40-45mph and beyond with great acceleration for bigger people. It is all about tunning the clutch and/or the variator. french bikes are an option too but seem to require more patience and money to reach the same effect as dual variated bikes.