I will go right to the rated spec as long as I have really taken into account, hills, speed, a trailer that is weighed when it is actually loaded including cargo, fuel, and water, and a fully loaded tow vehicle (including fuel, cargo and passengers). Many times, if you tow your full gross trailer weight, and, have a loaded truck, you will exceed your max gross load rating.

I always make sure to use a good weight distribution hitch that also provides anti sway like the Equal-i-zer hitch does so that you don't exceed your individual axle ratings as well.