Originally Posted by coldbike

I do run a derailleur, I have had mine set up as a 32 tooth in the front and a 12-34 cassette in the back. I had my wheel built up with a snowcat rim (from my parts pile), which means that I had no option to build my wheel as a 36 or 48 tooth wheel. I have had really good performance from my wheel since I had it built by a really good wheelbuilder, but if I carry more than about 35o pounds (plus me), I occasionally break drive side spokes on the rear wheel (like today). Since I live in Calgary, we have substantially less of the accumulating types of frozen stuff than you do. Usually, it gets cold enought here that the snow isn't sticky - kids can only build snowmen once or twice per year. Most of the problems I have are from the salt and gravel on the roads making things corrode. Full fenders help quite a bit, and I have wrapped my steering tube in old innertube to prevent salt spray from running down into the parts.
Wax or spray Pam cooking oil on your bike to give extra protection and help water to run off.
I have put serious thought into replacing the derailleur with and IGH and I may yet do it. I am not convinced that I won't break an Alfine though, I like to run lower gears than they recommend, I also carry big loads. I do know that the wheels build up much stronger and that under reasonable use they hold up fine. The Rohloff would be ideal except for the price and the fact that I don't need that much range on a cargo bike.
To put things in perspective, I just got back from a 9 day off road tour with my family and my CETMA. I stopped at a weigh scale on day 7 and the bike, me, my daughter and gear came in at 440 pounds. I probably started the tour at 460 pounds. This was an amount I felt comfortable riding on dirt roads for 165 miles.