OS Max .35 25 to 28% Castor
everything else 17 to 21% Castor.
I don't think there's such a thing as too much protection, but 17 to 20% is a good compromise between performance and longevity. 15% performance goes up, but replace the sleeve after 3 or 4 gallons. 30 to 35% and performance suffers, idle suffers, but the engine would prob. run forever.