One you left off the list is the Michelin AT2. Not as aggressive as the ones you listed, but very well in the snow and gravel roads. I managed very good wear, never had a problem on the gravel roads and worked very well on up to 6" of snow or packed roads.
I think the BFG KO2 while will have great traction will wear very fast with your heavy load.
Of the ones you listed, I think the M55 would be my choice if you aren't worried about a little tire noise. Most folks swear by them but a few complain about quick wear.