The XR is not so great in slush (but durability and puncture resistance are outstanding), but Supremes handled well when I crossed Monarch Pass in a snow storm this year - as long as the slush is soft enough so that the tire can make contact with the paved road. The Pluses are for when you want to minimize flats regardless of weight. They are very very heavy. I've never used the "normal" Marathon so I have no opinion.