A 2500 works just fine for a midsize fifth wheel. The new ones are the same as SRW 3500s with a softer spring setup in the rear, and you can address excess sag with timbrens or airbags if necessary (unlikely to be necessary with your proposed setup).
Fifth wheels do tow better than travel trailers, regardless of the hitch used on the travel trailer (imo), due to heavier pin weight and the hitch location on the truck. You also get a shorter overall package with the fifth wheel cause some of the trailer overlaps the truck. I won't repeat the line that many use that you can't feel it back there, because you can, but it isn't any more stressful or taxing driving down the highway with my fifth wheel than it is empty - it tracks extremely well.
I'd encourage you to check out Andersen Ultimate hitches. I have the rail mount version and it's a fantastic hitch both in terms of towing performance and ease of use (light and easy to install/remove).
