Try re-reading my above thread which was in the process of an edit while you were replying. Read it closely.
I'll try and clear it up for you. If Ford is calling only for a 20 grade oil in certain apps, then they want a 20 grade oil. If they call for a 30 grade oil they only want a 30 grade oil unless otherwise stated. Amsoil took the liberty of saying 0W30 was OK in applications Ford wanted only 20 grade oil for. If they call for 5W50, then use 5W50. Simple.
Another example my GF has an 08 Jeep it calls for 5W20, we know we can use 0W20, Amsoil says it is OK to use 0W30 as well as the other two. Jeep people say don't use it. Go to Mobil, they say 5W20 and 0W20, spot on.
You run your oil for 35K in that new Mustang? Or do you do what most smart oil companies suggest when under a warranty. You know, follow the OLM or the OM recommendations.
Again, I don't need to produce a warranty, I'm not shilling RL. I think its a better oil, and so do a lot of other people.
Also remember the topic here is "I'm sticking with RL"..