The only advantage I know of to run duals would be a higher payload capacity.
I don't believe weight carrying capacity had anything to do with the selection of duals. AI think a deuce with singled 9.00-20s will still carry more than it's rated weight.
One of the advantages claimed by the Army for a dual wheeled truck was the ability to sustain 5 flats (if the spare is included) during operations and remaining "mission capable" with no more than a tire position change.
The other claimed advantage was reduced overall height and reduced cargo deck height.
50 years ago, before the advent of roll on-roll off (RO-RO) ships, the Army was far more concerned with the height of equipment than it is now. As recently as the early 90s we still had to plan for deployments by reducing the height of vehicle to the lowest possible height. For planning purposes we were expected to remove everything higher than the steering wheel (cab, ring mounts, cargo racks etc) That's the figure we used to compute the total volume of hold space needed to ship the unit overseas.
All that said, and back to the original question:
I have an M35A2 that came from GL with singled 11.00R20 XLs and flipped hubs.
My other deuce is an M35A2C with 10 GI 9.00-20s.
The singled out truck goes better in snow and when lightly loaded; it doesn't spin the tires as much. The dual tired truck will carry more weight in soft ground without miring, due to better flotation (which works against it in snow)
The dual truck can carry around 6-7 face cord of 20" firewood in muddy contitions where the singled truck would mire with that load.
During the winter, when it's snowy, I leave about 1-1/2 face cord in the singled truck for traction and use it around the farm.
Lance