Im probably the only one to chemically have oils tested after Topspeed runs the oil that was still in Spec & lubricating 100% after such a test was Silkolene. Castrol RS was proved to useless & out of Spec within 2 runs. I use 5/40 for Topspeed running because that was best for the extreme test i put oils through for normal usage 10/50 . As stated its no longer called Silkolene but is the same oil.