I would go for the full cheetah. Yes its more money, but easier to get big power out of. Heres a few tips. dont get the 400pv, its not that impressive. The 421, 472, 485, 492 all use 4mm crank. Heres the good news they all cost the same price. Off the top of my head I think $2870 shipped. The down side is the 472, 485, 492 require the top case to be bored and ported, cost about $200. The cheetah pv is like having 2 250R motors on 1 bike. The power valves make the throttle responce like a 4 stroke. Lots of power from top to bottom. all I can say is hang on if you get one.