Johnny,
I know what your saying and in theory yes its about right.
that is one thing i hate when i hear people saying my car has a scale speed of 500 mph, even hpi are marketing cars with this claim.
I can see how you have come about your theory and i would like to see a video slowed down by 3.2 but personally i think once you have seen a 1/10th car go round a track "live" i think it would look slow or odd. Why not just give them a mabuchi 540 motor instead