I know the SM discussion was just had recently.  However, reading
through that discussion, it seems nobody mentioned this:

The "reintroduced" 15w-50 Mobil 1 oil is SM rated.  It is not clear to
me whether it has enough of the anti-wear additives, after reading lots
of pages online of various tests of the oil.  Mobil-1's site has
generally cryptic answers, which I don't generally trust.

I know there is plenty of dino oil with 20w50 or equivalent with no SM
rating and presumably the correct levels of Zinc, etc.  What about
synthetics?  Are there equivalent synthetics with known good levels of
additives?  (Castrol?)  Or does anyone have a good reason to think that
the Mobil 1 is still a good choice?