The people that designed these engines decided straight weight 30 was good. Then guys started racing ...higher oil temperatures...now let's say they lived in a cold area / region like Michigan or Detroit to boot.... so they used 20w 50.
All I can say is I would only go lower in much colder temperatures and for no other reason otherwise. I would go heavier due to extreme temperatures from high rpm operations or higher ambient temperatures and no other reason otherwise...Lmao..
No one should need to tell you what oil to use be a big boy do your homework ...and use common sense that can rebound of history.