Turtles, I've been saying the same thing around here for years, most just don't get it. There's no difference in trucks now a days between a 250/2500 and a350/3500 srw. A lot of f250s come with overload springs. With the same rear axle, front axle, motor, trans, and springs, that leaves a lift block being the difference and a sticker on the side.
The question that was asked of why anyone would buy a 2500 for a 5th wheel is inaccurate. It should be why would anyone buy a srw 3500 over a 2500. If you need more truck than a 2500 you need a dually.