How accurate do you suppose a GPS mounted on the bike is?
With my Duncan 403 Eliminator motor, 15 / 40 gearing, 18" holeshot MXR6 rears, on pavement I would max out right at 80mph consistently, according to the gps unit I was using. When using the same gps unit in a car with factory sized tires it paces exactly the same as the speedo.