I think you'll be fine. I have spent tons of miles in the snow with a dually and never really gave it a second thought or wished that it was a SRW in snow. One other item to consider though is freezing rain/ice. Just in terms of physics, wide or 2 more tires on ice, you might be giving something up in going to a dually. But realistically, I doubt that it matters that much. I would definately make sure that it is a 4x4 though.
I think the benefits of a dually with a sled deck outweigh any drawbacks.
Honestly, the only reason I dont have a dually now is that it is a dually all the time! You know, parking at the mall, going through a car wash, drive through, etc... All the times that you DONT want a dually.
But would I take one for towing/hauling? Hell Yeah!
Maybe they can make one with retractable wheels and wheel wells... Like a Transformer...