I have a CRF front end/wheel on my XR and had a 19" wheel built for street use and need a rotor for it. Have stock wheel for dirt. I see 270mm "oversized" rotors for sale but my instinct tells me thats not much bigger than stock and that I probably want 320mm. But then maybe I don't need 320mm unless I'm "racing" ?? I"m not, but I want good stopping power. Doesn't seem to be anything in between.