The max rpm for the 5.8 is listed on the Morini Franco USA site as 10000rpm. The 9.4 is listed at 13500 rpm. max . As for the sprocket issue, ask any member wh'se had a motor lock up on one of these bikes what happens. It's not pretty! Afreewheeling sprocket is much safer! BTW, my Staton hub is very high quality, and the HD hub is also. At the speeds these Morini's are capable of I'll pass on the solid sprocket. They are fine for motorcycles though, not for these motored bikes.And scooters generally use CVT's and are not prone to lock up the rear wheel in an engine failure.