Synthetic proponents, a challenge: Show me the performance requirements which a motor oil must meet to be sold as “synthetic”. Hint: there are none. A motor oil must only be manufactured using processes accepted to the marketing industry as synthetic manufacturing processes.
I think there ought to be advanced performance certifications required of premium motor oil, but in general we don’t have any. GM has a few useful supplemental motor oil standards, but “synthetic” is not a motor oil performance specification.