Depends on your trailer tires speed rating. Most ST tires are speed rated at 65 MPH. My LT tires are speed rated at 99MPH. So I tow what is reasionable and prudent.
I'm a low 60's kind of guy. I keep to the right, leave reasonable following distance, and don't drive when very tired. Hard to believe how fast I've gotten old!
Between 60 And 65. Its a VACATION. If we are in a hurry, take the car and stay in hotel. Try and live by the 330 rule, 330 miles or stop at 3:30. Did I already say its a VACATION. :)