Understood but respectfully I never asked for advice on the BMW. I have owned that car since 1997 or 1998 and have overseen its maintenance and repairs since that time, or done them myself when time permits, together with about half a dozen other BMWs since the early 1990s. This includes a few endurance race cars that would regularly see high RPM operation. I am very comfortable sticking with the original, non-CAFE influenced oil viscosity recommendations in the owners manual. Again, with all due respect, if anyone saw the condition of the crank (when we have pulled the oil pan to fix the leaks that come with BMW ownership) or the valve train, you guys wouldn’t be questioning this approach either. Oil pressure is a critical component of engine longevity, and the engineers who originally specified the oils this motor runs on set the viscosity the way they did for a reason, with main bearing clearance and operating temp in the sump in mind. For this same reasoning, you won’t find me here asking if I should use a higher viscosity oil in a newer car like my Toyota or the Ram - if the engineers who built the car are frankly too stupid or dishonest to specify the correct oil viscosity (even accounting for the regulatory framework of CAFE and other requirements), then the answer is find a different manufacturer. All that said, anyone who wants to buy an M20, M30, or M60 powered vintage BMW and run 0w or 5w oil in it is welcome to do so - it is their car and their money. I am going to stick with what I have been doing as it works well and is in alignment with the advice of the people who built the car originally.
Have a good weekend.