Watch the Amsoil videos with Gale Banks on Youtube lots of good info. They show whatever weight oil you put in shears down pretty fast to next weight down then the viscosity returns over time . Plus the 100% synthetic flashpoint is higher. I like the Motul gear oil and brake fluid so i decided on the 5w40 its made for small displacement higher HP engines. Being tuned , running the snot out of it , and Higher arizona heat , narrow rod bearings , was my decision . I ran 5w40 in tuned and modded 2014 Tremor for 35,000 miles never had a issue . If i was still all stock i would be running 5w30. Next oil change before summer will be 5w50.
28 min mark to end most interesting about 5w30. 37min mark graph talks about shear