Main things that affect top speed:My top speed was about 100mph and my average MPG is around 61
Altitude above sea level.
Barometric pressure at the time of the run
Tyre pressures and tyre rolling resistance.
Fuel octane rating.
i found that standard gearing was hard on the bike at high freeway speeds and went up a tooth at the front sprocket and down 2 teeth at the back. This lowered the revs substantially and made an even bigger difference to the already excellent MPG 80 MPG (Imperial) standard ratios is not uncommon if driven gently