If you are thinking fifth wheel and new pickup, I would select the F-350 SRW over the F-250 just for the extra cargo rating. This will give you the cargo capacity to carry a generator, or anything else you might want to carry.
Also fifth wheels tend to get heavier as you get closer to putting down a deposit, 'honey, this one has a electric fireplace, and larger kitchen' = that sort of thing.
Of course if you already have the fifth wheel in mind, then you will know the exact weight of the trailer, and pin weight 'empty'. And you will know if it has a forward or rearward mounted fresh water tank. Normal 60 gallon tank is about 540 pounds, and that can be split equally between the trailer axle and pin, or more on the pin, or not, depending on how far forward the tank is to the hitch.
Many get surprised when they buy a 2500 truck that 'can tow anything' and then find out that they meant anything under 1,500 pounds of pin weight. The F-250 has a slightly higher GVWR, and they tend to be able to carry 400 pounds more with the gas engine, due to lighter curb weight. Still a crewcab is about 400 pounds more than the regular cab, and you did not say what you are looking at.
Have fun shopping!
Fred.