I will be at 0w-30 with my 100000+mile short block castrol syntec makes this german oil that is greenish in color that is a very good oil to use. I had a friend that had some sheets saying how good some oils are to others and this one came up as number 1.You have to think when your car is cold your oil is thicker.You start your car and a thick oil will be more harmful then a thin oil. Now most of you will say what about when your car gets hot? Will the oil break down faster? nope thats the reason for the syntec technology. They have found something that will not break down their oil at high temp's and also last longer going to every crack and groove.but thats my 2 cents

ps: I have used amsoil for a while and I love it. But my friend had this castrol oil and i feel in love, so its all up to you.