I have to say this - do you guys drive with handbrake on?

?
38-39 is not really a problem in everyday driving BUT there are so many factors influencing the cons that is probably pointless to compare.
Just to mention a few:
driving style (acceleration, costdown, gear selection, idling), weight of the car, tyre pressure, outside temp, AC usage, heated seats, number of people in the car, oil you use, fuel quality...
I do these figures for living and I can tell you there is a reason why everyone wants to keep them (and related CO2 figures) as low as possible - from marketing to road tax to cong charges.
Just because you you can't drive it this way / don't want to doesn't mean it's impossible.
P.S. I see the future and in a new topic a couple of months "Why are my tyres bold after just 5000 miles?

?" "can they last 10000???"