I went to mex via I8 yesterday and the signs posted said trailes nothing with all vehicles.
Again 55 may turn your boat but it is a hazard in a lot of situations particularly if not in the far right lane, then it will also create other problems. Too many try to self enforce speed limits and create hazardous situations. Last night some clown pulled into middle lane of I10 (75mph) at 55mph with his trailer and I almost ran into him. It didnt help that his trailer lights were out either. Cops too busy trying to stop 18 wheelers (same point in time) and let the clown slide by. Big truck didn't appear to be doing anything wrong IMO!
Bottom line, drive what you think is safe for you, but remember there are others out there also. 5 or 10 over is generally ok with most leo's, bumpy my speedo is 3 off from the computer (scan gauge reading) 4-5 by GPS!