I also could not get any definitive answers
My set up now on the GP is
R56 drilled and slotted rotors with R56 Pads - been on for 500 miles
R56 pads are the same shape size etc, appear to be a different material but are 50% of the price of
JCW - probably due to volume of manufacture as they are standard R56 cooper S pads.
Car stops very well, but then again it did on the standard set up. I need to give it some track exposure or consistant fast heavy road use to see if they fade.
Alan