Taking the bike back to it's home today I hit 70mph in 3rd and topped out at 81mph in 4th. Motor was not tached out but had no more power haha. It might go faster if I held the throttle wide open and waited FOREVER or I could probably get 5mph more by changing sprockets but I'm happy with it. It can handle 75-80 no problem were as my stock 3 speed 45" blows head gaskets if I hold it at 70mph and is most comfortable at 60mph. So the little bit of engine work and using a 4 speed gained about 15mph.. worth it ? doesn't sound like much but It's the difference between a 45 you ride in town vs a 45 you can take out of town. Having the extra gear also makes it much quicker getting up to high way speed.