I work for a Canadian company driving a 2006 FTL Columbia. It's limited to 65 mph on foot and 62.5 mph on cruise. Recently the management started complaining about our poor fuel mileage and they turned down the governor to 62.5 mph (!) both on foot and cruise. "Show us 6.5 mpg and we'll turn it up back to 65 mph," said the fleet message on my satellite.
So, even governed at 65 our trucks had very poor mileage! Which is understable to me because:
But when I buy my own truck I'll probably stick to 65 mph where it's allowed. I think at 70 the fuel cost outweighs any time gains....