I have a similar post on the mountain bike forum, but someone suggested I ask here as well.
I have a Trek 930 with 26x2.0 Nokian studded tires (the 106 stud model). Lately I've been riding on the snowmobile trails in the area, and have been pleasantly surprised at how easy it is. As long as it is cold (below 15-20F), the trails are packed enough that I don't sink in too much and can average 8-10 mph without much trouble.
A long term goal is to build up a Surly Pugsley and really enjoy these trails, but for the time being, I'm wondering if switching to fatter mountain bike tires would make a substantial difference. My current 2.0 tires feel more like 1.8 or 1.9 to me, and I think I could fit 2.3 or 2.4 on this bike. I'm looking at Hutchinson Pythons in a 2.3 size, no studs, just floatation. Any thoughts on whether slightly fatter tires would make much of a difference?