hey guys, just found this thread and thought I would throw my 2 cents in.
We used to run M-55's on all our service rigs (1 ton Fords and Chevy's, all around 10k lbs+). They are quiet on the road and wear like steel. Unfortunately that is also the disadvantage for the conditions we drive in. When things get cold and slick they grip about as well as a chunk of steel too. I have 315/75 Toyo MT's on my 80 now and find they are about the best mud tire I have ever driven in the cold weather and on ice. They definitely throw more than the 55's did and are louder for sure, and I am definitely not expecting as many km's out of them.
All our service trucks now run Goodyear Duratrac's on them. They dont last nearly as long but its better than hitting the ditch
Dont take me the wrong way, the 55 is a great tire just make sure the conditions warrant it.