Right now i'm running Castrol 10w-30, but as we enter approach January i'll be running my Audi 90 CS (2.8 v6) when temps are going to be 20 or 30 degrees (F) below zero. I know Porsche now recommends 0W40 M1 for all 911's, but before I made the switch I just wanted to get some opinions or see if anybody uses the product.

 

that is exactly what 0W-40 full synthetic is designed for ( very cold weather ) and high performance cars like the porsche