For those of you with these beautiful 5th wheels, what your max weight and length. Also are you pulling with gas or diesel?
I tow heavy loads with diesel trucks. Gas engines work too, they just go slower up hills.
When towing 5th wheels, length doesn't matter as far as the tow vehicle is concerned. It's all about pin weight. My personal limit for towing with an F-350 SRW truck is a 5th wheel with a GVWR of around 15,000lbs because that translates to a pin weight of 3,000-3,300lbs. When you add the hitch, cargo, extra passengers, etc you will be near the payload limit of an SRW F-350 diesel.
All other things being equal, the 7.3 gas truck will have a higher payload rating than a diesel so you could go up to a 16,000-17,000lb GVWR for the RV without exceeding the payload rating of the truck. Just rough numbers here. There are many variables depending on how the RV and truck are loaded.
Having said this, a LOT of people tow 20,000+lb toy haulers with F-250's.
Length of the 5th wheel only comes into play when your 5th wheel is too long for national and state park RV sites. Anything over about 35' is generally considered too long. You will have no problem with long 5th wheels in most private RV parks.