Hmmm, probably right. As a guess, I've probably been averaging ~40mph overall, so I may have ~10 hours on it so far.
You may be being a little optimistic there. My business car spends reasonable amount of its life being thrashed up and down motorways, regulalry in excess of 70mph, and yet over 4 years and 40k miles the average speed is not much over 32mph according to the computer.
To average 40mph you'll need to be doing 80mph for the same aamount of time you are stationary. Not impossible, of course!
