Interesting read: https://blog.amsoil.com/how-much-syn...-is-in-my-oil/

I lived about an hour from where Redline is made. Every private or amateur racecar at Sears Point Raceway ran it. Could almost run a oil line to the track. I joined in.

HTHS is crucial but not the only metric for choosing an oil. There's about 10 performance benchmark tests. Some are mandated, some elective in testing.

For fun looked at Redline and Amsoil the other day for their respective OE 505.01 spec 5/40 European lubes. Near identical to the untrained eye. Oddly Redline has a much higher (11%) NOACK burnoff. It also has slightly less viscosity at the 40wt rating in Kinematic terms which is far more accurate. I recall HTHS being the same/close at 3.8, including VI @ 168 (extremely high). TBN is limited to about 8. This is just slightly above 7pH being neutral. If splitting hairs Amsoil has the advantage.

I'm not sure Redline exceeds the HTHS by any significant margin, other than a margin.

Far as the 505.01 spec goes I avoid it due to reduced SAPS PPM's and reduced TBN. TBN really plays into the final acidity levels. I've seen UOA's where TBN was flagged. Most OE specs oils become so acidic it attacks engine seals. Helps cause oil leaks. It can even eat away at engine bearings. No fun. I prefer "unregulated" oils allowing higher TBN levels. Even Amsoil mid grade 5/40 Euro is at 10. The 5/50 is pushing 13. I challenge anyone to find it any higher- if we're doing the challenge thing.

We tend to get so wound up on operational/running specs it's easy to forget most engine wear occurs during startup. High SAPS/Zinc PPM's are crucial no matter the oil Group type. End of the day protecting the engine is first priority in my book.