Here's a challenge. Contact your vehicle manufacturer ad ask about stopping distance from 50, 60 & 70 mph. Then ask about the distance if pulling your XXXX ton trailer?
If you say "Ya but I have brakes on the trailer" I would ask if you have the brakes set so that your stopping distance at 30 is the same with and without the trailer? I wouldn't test at any higher unless you have done a 30 mph emergency stop.
60 mph = 450 to 500' with 5th wheel
How far does it take you to stop?