i don't know. you can't figure out that kind of stuff without knowing the gearing and other crap. he got destroyed by a 500cc utility quad (in another video) so it's not super fast (i'm sure he's still doing 40+ and quicker than most mini bikes).
i'd rather take a 5.5/6.5 and do some mods so it's making the same or more power.
you also need to consider the weight with that. there's no way i'd want to be picking that thing up to stick it in the back of the truck.
think about it, if this was a really good idea wouldn't people be running the 13 horse motors instead of the 6.5s?