ST tires are speed rated 65 mph (most) so 65 it is for me. Towing above 65 (unless tires are rated more than 65) is playing with fire and asking for a blowout, esp. the more you do it and the faster you travel. I use our GPS as a speedometer and run at 64-65 mph and max out at 65.0 mph. Sometimes it's so easy tho. to drift above 65 if not watching speed closely, like when cresting a hill and I brake and if needed, downshift on steeper grades. Even if a person could go faster, 65 seems to be a good max. considering all the potential factors, including a driver's age.
It always surprises me how many figure they can rely on their made in Ch*na brakes to save them some day if in an emergency/panic situation but will gladly condemn Ch*nese tires as being garbage. Some don't even ever check their brakes at all. Factory wiring and splices can be substandard too.