The cast iron rotors are going to have to wait until next Winter's mod-fest. So I am thinking of upgrading my '01 748/870 brakes with a Brembo GP Master Cylinder in the meantime. Is this a worthwhile upgrade to make before going the new rotor route? Will the radial master give more breaking power or just improved feel? And for hard street and occasional track day use which one is best, the 19x18 or the 19x20? Any installation tips or do's and dont's?