Personally don't care for super single, limited tire choices and based on the purpose of the tire & it's extremely stiff sidewall I imagine it would ride similar to a normal dually setup.
For our purpose of burning up the road getting to and from adventure spots, some gravel backroads, fire roads etc the 3500 was better suited for our needs. We have a heavy build and the van feels quite stable cruising down the highway and the extra width of the duals helps stability in strong side winds, this I can attest to as our previous van was a low roof 144 pop top.
If we planned on doing a lot of backcountry exploring then the 2500 would have probably been a better choice based on the single rear wheel.
I upgraded the rear shocks to Fox with the heavy valving and that made a huge difference, also added Sumo springs up front which helped. While the van rides great on the road I may upgrade rear springs at some point to see if this helps soften the off road manners.
Hope my .02 helps and sounds like either way you'll have yourself a sweet new rig.