I have been following this topic with much interest. Disclaimer, we are in the 63-65 MPH range when towing. One thing that I have not seen mentioned is controlling and stopping the trailer in an emergency situation. Some trailers are equipped with disc brakes which makes panic stopping much easier to control. However the vast majority have the OEM electric brakes which basically doubles, or more, your stopping distance. I have also seen more trailers than I care to count with noticeable sway when they pass me at considerably higher speeds. I just hope I am not in the way if they lose control. I have seen first hand what happens and it never ends well. So for our best MPG and comfort level for controlling and stopping, we will continue in the 63-65 MPH range. We are cognizant of faster vehicles overtaking us and do our best to stay (get) out of their way.