Lovely. I've never ridden an offroad bike but I'm thinking about getting one.
I was reading about motorcycle Grand Prix and they had a 125cc 2-stroke class (it's now a 250 4-stroke class) and those bikes run 155mph on a 125cc motor--7 cubic inches. 7 cubic inches and 40hp. A 5hp Briggs is 12 cubes. It's amazing how much power those little motors make.
Honestly, it was tough learning to ride this 250. All of my vehicles are diesel: a bus, a crewcab pickup, a 15-px van--even my Passat I shift at 2,000rpm. The fuel injected 250 in my bike runs well at low rpms so I just shift it like a truck and it seemed weak at first. Then I started experimenting with the revs and realized that if you drive it like you hate it, it makes lots of power. The diesels make short, heavy pushes between shifts. The bike likes long, screaming revs.
I can see now how an 80 or 125 would easy do the job in a bike. 155mph with 125ccs? Damn.