.040 will not cause warping. Not sure when that occurs or what compression ratios. A set of untouched heads and "10.5" compression ratios would blow OEM head gaskets, and we would just mill them .020 block side and .019 intake side and be done, when rebuilding. While you were at it you could go .040 and get down to min NHRA cc's. I never went farther than that and never blew head gaskets.