If your ever going to pull a 5th wheel over 10,000 pounds I wouldn't even think about anything under a one ton DRW. I've done the numbers on a Ram 3500 MCSB 6.7l ASIN transmission 4X4 DRW with both a 3.73 and 4.1 ratio with a 1,500 pound payload consisting of two adults, two large dogs, hitch and misc other payload which makes the GVW around 10,000 points leaving 4,000 pounds for pin weight. Based on those numbers the max you can pull with either the 3.73 or 4.10 is 20,000 pounds. Anything more and you're going to be overloaded. Sure you have a lot more pulling power but you're limited by 14,400 GVWR which has to carry the truck, you and your family plus your pin weight.
If you start with the same rig with SRW you start with a GVWR of 11,500, if I remember correctly. That's only 1,500 pounds of pin weight which at 20% is a 7,500 pound rig. Even if you limit your payload to 1,000 you only get to 2,000 pounds of pin Which is a 10,000 pound rig. You can drop to 15% pin and get a little more but is it worth it?
Considering the small price difference between a three quarter ton to a one ton with the same engine configuration plus the even smaller difference between SRW to DRW why risk being overloaded and limiting your considerable investment.
Here is a
link to my calculation for the above with a 4.1 ratio. Check it out for yourself then play with the numbers for your own configuration.