I don't know much about the MTRs, but a pretty common complaint about the Duratracs is that they have lower than average tread life. I think a lot of that is due to the winterized rubber compound they're made of - it's a bit softer and doesn't wear quite as well as a normal tire.
Mind you, the Duratracs are 6 years old now. When you compare them to newer winter rated tires like BFG's KO2s or Nitto's Exo Grapplers, both companies are promising significantly better tread life. I'm assuming that's because they've come up with better rubber compounds since the Duratracs were released that are longer wearing yet still keep good traction in the cold. That said, the KO2s and Exos are only just coming up on a year since they hit the market, so it might be a bit early to find a good long term review to compare with.