Even more modern speedos are much the same. For example, my F650 speedo (cable driven off the front wheel) reads 10% high from 40 - 80ish. The odometer checked against my SS1000 mileage was within 1.3%
Based on the few Interstate jaunts on my ST where I had a good idea of the traffic speed around me, its speedo is very likely the same 10% optimistic.
(Now if I can just out to the garage and finish that transmission project on the ST - been down with a virus all week