I tried cross drilled rotors on my 500E. If I had not performed a thorough inspection of the brakes between run groups at a track event they would have failed. They had been drilled and champhered. You cannot champher the inner portion of the hole. Factory brakes are cast with the holes and then drilled as a finishing operation. Check out cars at a track event. No one with big fast cars uses drilled rotors. They are beneficial under wet track conditions and are used by ralley cars to improve initial brake response under the really adverse conditions they encounter. They do work on motorcycles to help reduce the gyro effect and aid in turn in. For street use they would probably help initial brake response under wet conditions. Normal street use will not tax the rotor enough to induce failure.