Penz Plat/Ultra here as well. My cars that burn oil seem to burn much less on PP/PU. Also drive quieter and smoother. M1 I've used before but has not fared well. I seem to burn through M1 considerably faster on my Subie engines. Even Castrol fared better and during an engine rebuild/reseal, the engine was nice and clean after 10 years with Castrol.