I haven't used Amsoil since I had my Eurovan, when I was basically driving for living. I was doing about 25-30K on 0W30 SSO, no filter change and about 3 qts. top up oil during the run. Most of that was hwy miles, though some traffic/idling.
The van gave up around 250k, but the engine had nothing to do with it. Unless, of course, Amsoil were better at fixing electrical problems.
I also used it in a '93 Nissan SE-R, 20K OCI's. That car had a really small sump, so I wanted to use the highest quality synthetic I could find at the time. It served the car well. It was well over 200K when the person to whom I sold it ran it into an electrical pole.