I don't go by the mic for rotors. I go by whether or not they are heavily grooved and/or have a lip on them at the outer edge. I won't have the rotors turned either. To me, shaving off the mass of the rotor seems like a good way of removing its heat sinking capacity. I'm pretty anal about stuff like braking ability, so take it for what it's worth. I do the rotors every two sets of pads. At 48k, the lip on the outer edge was significant.