I want to put this question to bed, as it has been debated several times over various forums, and still yet to make a decision.
My 08 Ram 3500 SRW has a GVWR of over 25,000, with about 6200# GRAW; the dually is 3000# more, but is rated to haul slightly less, due to the weight of the dual wheels.
We are looking at upgrading from our current Salem LE Sport fiver, which is around 12k when we camp (close to 20k combined, and well under our max) but are very close on rear axle weight; 2700 unloaded + 3000 hitch + 1000 transfer tank, or 500 over at 6700. Down the road, we will be looking into a FT rig, where pin weights can be over 2 tons in some cases.
The fix is wheels and tires, but which way? The 19.5 245/70 L/R H are rated for nearly 5000 each, along with the rims, and 5 mounted, balanced and shipped would be $6773 from Rickson (just FYI, as I haven't been able to contact any local HD tire shops in my area). A dually conversion, which includes 6 Eagle alloys, front and rear adapters and custom Mega Cab dually fenders to fit the 8' box, would run $4521, plus labor to install and paint the fenders, maybe another $500.
The 19.5 would be a direct fit, end of sentence. However, I can imagine the headache of getting replacements, and possible foul weather traction issues. The dualls will be 17", which means easy tire replacement, but then I'm stuck with an extra set of tires sticking out the side, along with the extra girth. A bonus is the wider hips line up better with the sides of the trailer, so no more ugly brick staring at me in the mirror, and maybe a bit better airstream.