Mobil Super 5K is a heavier sodium oil with no moly/boron....like Valvoline and some of the specialty oil companies like Schaeffer, Brad Penn, Royal Purple, Lucas,...and also Peak, ProLine, Traveler, Adv Auto, O'Reilly's, etc. I suspect ST would have ample Moly and Boron. Depends what you're looking for and have confidence in. MSS is more like PP/PU. Mobil 1 is the only remaining heavy magnesium oil in their 20 and 30 grades. Their M1 0W-40 doesn't have magnesium and generally matches the makeup of PP/PU/Castrol.