I've come to the conclusion that once the contact patch is coated in dead skin cells, wax globules and powdered truck dust, the formula and duro don't matter anymore. Up until that point, a quality 95-97 is nice. Even 99 f4's are doable. Oh, and treaded picks up more shit, so maybe wheels that have been ridden in the wild and have imperfections on the riding surface will load up faster, too. So maybe keep a set of fairly pristine 95-97's for riding dusty death trap parks?