How fast do you go

We tow at 3 mph over whatever the limit for towed vehicles might be. I went to the trouble of changing the trailer tires to Endurances specifically so as to not be limited to 65. I am always confused by the statements that someone is not in a hurry to get anywhere. If I am going at all, I must be going somewhere to do something. Whatever that something is, it certainly isn't being done sitting in a truck cab. I'm jealous of those in states with higher limits. If I could, I would cruise at 75. Mileage? I don't even check. 18,000 lbs. and the aerodynamics of two 4 by 8' sheets of plywood being shoved down the road sideways. Whatever it is, it isn't good.