I have a 39.5 foot 14,100 lbs 5er and pulling it with a 2015 F350 SuperCab PSD SRW with 143.5" wheelbase. Everyone one of my numbers are under but real close and here is my scale weights in Towing Planner. Actual Weights - Fifth Wheel Weights from CAT Scales - Towing Planner
I believe that even with the numbers are OK this 5er is to big for my my truck. On a nice calm day it tows great and it has more power then i need but it should since the same engine that is the F250, F350, F350 DRW and the F450 DRW truck. But with side wind it hard to keep in your lane and some gusting winds can be white knuckle. Yesterday we solved that problem since next summer I want to travels will be over 15,000 miles we purchased a 12,100 lbs 5er that is not as tall and 34'11" long. We still going to be at the upper end of the weights but less of profile on the windy days.
We have decided that we would rather deal with a smaller 5er rather then the DRW and long truck.