Hi there :)
I'm new to this forum and am amazed at the variety of opinions on this thread.. Just bought my TT in November and have spent very little time towing it.. but I think that you have to address each point..
I spend a lot of time on the interstate and surface roads because of my job and tend to have a heavy foot..
So I'd like to address a couple of points:
1) driving faster than the rated speed of your tires is looking for trouble, especially when heavily loaded.
2) move with the traffic if you can but if not, get over to the right.
I've seen 2 and 3 mile backups because of people driving significantly slower than the speed limit, sometimes in the left hand lane, frustrating other drivers, who do stupid things !!!
3) make sure you have enough stopping distance. Tail gating is suicidal. Are your brakes in good shape?
4) Try not to ride along-side of cars or 18 wheelers.. giving yourself and the others some room to move if you encounter a pot hole or road hazard.
5) sometimes it just makes sense to slow down. Slick roads, pot holes, high winds, heavy traffic. Why stress yourself out trying to fight the road conditions?
I like to drive faster than the speed limit without my TT and was pretty comfortable pulling the unloaded TT home from the dealer at up to 70 in the interstate, but that was on an "open road", Sunny day, slight wind gusts, with TT tires rated at 75 mph..
But I pretty much stayed between 60 and 70 primarily because of the traffic flow..
So I guess that the answer to the question as to "what is a safe speed" is to ask yourself what am I risking driving this way? I couldn't live with myself I my actions caused some one to be injured or even worse, lose their life!! So let your conscience be your guide.. :) You will get there when you get there.
That's my 2 cents worth
Just remember you don't quit playing because you get old, you get old because you quit playing!!:B