Depends on the state. In CA for instance, it is 55 mph, anytime anyplace, any trailer. In UT, if the road sign says you can do 75 mph, you can do 75 mph.
As a practical matter, wind is going to be a big factor in maximum speed as will altitude and grade. So will truck capacity -- 5ers tend to a fair amount of frontal area and wind resistance increases geometrically above, say, 60 mph.
If a tire blew suddenly, would you feel confident that you could safely get the rig stopped? Nobody ever plans to have this happen, but it can and does, even on new tires. Say the driver in front of you fell asleep and lost control of the vehicle and you had to make a sudden stop....would you be more confident at 60 or 75?
On a 4 lane divided highway with little wind and minimal traffic, I'll allow myself 65. Otherwise, use common sense and adjust for conditions. Getting to your destination in one piece is always a good thing....even if it's 20 minutes later than you planned.
I have driven professionally all my adult life. It sound to me that you have answered your own question. You have a speed you are comfortable with. Stick with it. You have to be comfortable or it ain't no fun.
I will second the last poster. The maximum towing speed depends on a long list of things. One is the ratio of tow vehicle to towed, One is the design of both (high or low profile) tires, (on both) weight distribution (On both) slill of the driver, various stability options and safety options and run flat options all add to the factors. Road conditions are part of it.
Bottom line is if you feel uncomfortable SLOW DOWN
Another thing to remember is the phrase "Basic Speed law" this is the speed at which you can fully control your vehicle.
I see folks who have a drink or two... If you have had a drink recently (Alcoholic of course) then the basic speed limit is parked that is zero point zero mph, parked Even if it's just one drink.
Figure 2 hours per drink plus an hour of safety for the average person till you can put the key in the ignition That is MINIMUM
Just a few thoughts,
1. Aren't we in the RV thing because we want less stress? Driving a comfortable 60 to 65 is a hell of a lot better than white knuckles at 70 -75.
2. Most of us are on roads we are not familiar with, especially as we approach the Campground, turns come scary fast at higher speeds, don't they!
3. Fuel costs and wear in the rig ET all at higher speeds are just not worth the time savings.
4. I suggest doing the math - an extra 10 MPH (probably average 5 MPH really) gets you in 20 minutes earlier at the end of the day...see # 1, save the Excedrin headache!
5. Excessive speed is a Pi-- poor substitute for proper trip planning!
With the understanding that I do not drive often in California,,,, I see no need to violate the speed limit by more than 5mph most days.
If the speed limit is 55 and folks want to drive 75, Well, that is their problem. I recall a 9-1-1 call I got one day complaining about one of my State Police Troopers (Who's name by the way was also John) seems he was driving exactly the speed limit and nobody wished to pass him cause they feared a ticket. The idiot caller was complaining that he was going to cause an accident by not allowing him to violate the law... I still wish I'd ask for his name and driver's license number so we could submit the tape of the call to the prosecuting attorney in the county but I did not, I transfered him to my sgt, identified the trooper and when the sgt came back to find out who it was ask if he wanted me to relay a message.. .Suggesting "Good Job" as the message (Sgt agreed)
I have also read the instant gas millage on this ride and it stays fairly good till around 55, then it starts to drop, and around 65 it falls like a rock in free fall. 55 is good