Please forgive my ignorance here fellas, but does anybody remember the last TSB that came out specifying the viscosity for our cars?

I've been running synthetic 5-50, 15-50, and most recently, Aggip 20-60 synthetic racing oil. I've found the 20-60 the best at keeping temps down, but I worry that it's toooooo thick to lubricate properly. Also, I don't know if it has the proper amount of anti-wear attitives, detergents, dispesers, etc....

What weight would you guys recommend, staying with a full synthetic? I live in a climate similar to NY state and the car is not driven in the winter, only hot humid summers. It's never raced, only driven hard from time to time. And would it be SL, SG, SJ certified?

Muchos Thanks