Beyond tire capabilities, I think for each individual, and each set of conditions, the max speed varies greatly. Personally, I don't believe any trailer rig or motorhome with toad should exceed 70 for any reason, regardless of the relative skill of the driver or traffic conditions. If and when a tire blows out on the TV or motorhome at those speeds, it's probably less than 50/50 chance of avoiding a bad accident. As the speed drops, those odds change dramatically. I think everybody has to decide at what speed they are comfortable, and it is always advisable to be aware of speed limits. Unfortunately, here in Ca, that means 55 for anything being towed. That may work for a 73 year old with a 42 foot behemoth towing a Suburban, but for most alert people, I think that's too slow. I think it tends to encourage distraction and multitasking while driving, which isn't good either. I regularly exceed that. But these days, it's not by much. I am learning that the journey is half the fun.
So, I think there is a range of reasonable speeds, depending upon conditions, and there are lower limits as well as upper ones, which define safe and sane speeds.
2006 Jayco Seneca 34SS
2006 Jeep Wrangler Unlimited Rubicon Toad