i grooved my MT/R's cause they suck in the mud. the grooving helped... but they still dont come close to a TSL, lol!
worth it though. thornbirds have a lot of meat to groove. so i say go to town with the grooving iron or get them siped.
look over your tread and see what you can take out. more grooves meen more edges to grab. the more open the tread is the easier it is to let go of mud. but the louder it will be on the street, and i noticed i pick up more small rocks then before.