Paul,
With Silkolene 10w50 Pro S being on the market, why are you even considering anything else ?

Rod has chemically tested most of the oils after high speed runs (Castrol RS was rubbish ) and the only one that showed NO degradation what-so-ever, was the Silkolene. In use, I also found the same thing as Tabetha has mentioned with the Amsoil tests on the Mobil 1, in that after a very short period of time, the oil pressure started to drop (especially at high temps).

I can even bring you some Silkolene on Wednesday for you .