When I went out west with our trialer in 2005 my Wife was driving and I notice she was going 80 or so, then a few minutes later I said "OH my, your going 90" and she and I had no idea. Of course there were no cars around, so it is hard to judge speed.
While driving on the Interstate I get it up a little past 90 to pass and it does not seem that unstable to me. Of course I have never tried to go faster than that.