So my family bought a BAB (big ass boat) before thinking about how they were going to tow it. The boat and trailer weigh 6200 lbs dry, which is in the annoying grey area between a light duty vehicle and a full size one. Case in point, I have a Gx470 with a 6500 lb tow rating, my brother has a Tacoma with a 6500 lb tow rating. We both LEGALLY can tow the boat so long as we stay in the payload limits. But would you tow the limit 150 miles over mountain passes?
Specific question made generic - Whats your safe margin of error for tow ratings? Would you feel safe towing the limit? or would you always give a, say, 15% margin? Typically I like to stay about 1500 lbs under the limit, that seems to be where a tow vehicle is happiest. but what about you?