If money was no object, I would put the largest motor that would fit in there. I think you would like the extra horses, I know I do, it makes the bike easier to ride. I have a 5 horse flatty and a 6.5 clone. The clone is much smoother. I weigh 210 and ride mostly in the dirt with small hills. Pavement isn't that much difference with the two. The flatty isn't a smooth takeoff, it is either on or off the throttle. Part throttle or throttle control while maneuvering is much easier with the clone. Both engines are stock.