When I shop for a truck the first thing I do is look at the little yellow sticker usually located on the door pillar on the driver's side. It will tell you how much cargo capacity there is for that particular truck. I was really hoping to get a srw last time around but most of the Ford diesel srw's in a King Ranch or Platinum had around 3200 pounds of capacity. The loaded hitch weight of our fifth wheel is 3100 pounds. Add the hitch at 180, us at 300, our 25 gallon auxiliary tank at about 240, filled, the 2 Boston Terrors at about 50 plus food and drinks for the day and we are suddenly bumping 4000. I could have gotten a different truck with less options to reduce the weight but not what we wanted. The dually has almost 5300 pounds of capacity.
I know most will tell you how much more stable, etc. a dually is when towing but honestly I cannot tell that much difference. We have owned several srw's in the past so I have experience with both. Our last srw, which towed our current trailer, had great road manners but we did experience a lot of chucking, probably because I had too much weight on it. That went away with the dually.