I agree with Desert Captain on minimum cruising speeds. You need to maintain the speed limit at a minimum or you are a hazard to yourself and the people around you. There are different speed limits depending on if you are towing or not. When on flat terrain straight interstate highways, I pretty much cruise 5 mph higher than the posted limit, just to be less a hazard to the people around me. But my personal limit is between 65-70 mph. I could go a lot faster but I have fuel efficiency on my mind.