why the hell do you want to rub all the white paint off? and what are you planning on painting it with? . if the white paint isn't cracked or scratched through to the plastic , don't waste your time , if your worried about the silver chipping off and white coming through , that only happens if you don't face it back properly (i.e make sure you get in all the little corners etc , even if only with scotchbrite) , facing off to paint , i always use 600 to start and go over it with 800 (painting 2k) kr4 is a prick of a colour if your not expirienced with painting (have you ever seen a silver car that looks kinda splotchy= bad painter=looks shit) .