I took a quick look searching F550 and RAM 5500 specs. Specs on the F550 shows 4x2 towing at 34,000#. Ram 5500 35,200# Both with the diesel engine.
I have the 5500 with 60". Sometimes would like the extra length/storage that would come having the longer version (Utlility Bodywerk bed, Kelderman Air Suspension system all 4 wheels). But it is also my daily driver. So 60" is darn near perfect.
Towing a 42' Majestic. Trailer with full fresh water shows 27,000# on the scale. Pin weight at 4900#. I have the Gen-y Torsion Goose Neck. Tows and rides great.
Gary 2021 NH Majestic
Ram 5500 with Bodywerks bed
Box Elder, SD and the road