cas951,
It is funny, hearing different reccomendations on oil from 3 separate sources that I all consider reliable - very anal enthusiasts, porsche AD, and the car's manual itself
When did mobil 1 introduce its 0W-40? That might shed some light on some of this. I'd also assume that 0W-40 is best for cold weather and has the best flexibility for high temperature variance.
How about opening a open in poll on oil usage...such as 5w30, 10w30, 10w40, 15w40, 5w40, 0w40, etc and see what people are putting in thier car?