to each his own....mobil 1 full syn would be more than ample for your application, even on those mountain runs, if youre so concerned about it then just change the oil after your fun, i know of anal people who would do oil changes after hitting the 1/4 mile a few times

as for castrol...heres the lowdown...

"A word about synthetics: Only oils that are created using Poly-Alpha-Olefin based technology are considered to be 'synthetic'. At least by anyone who knows better. The Castrol 'Syntec' synthetic oil is actually just a much more thoroughly refined 'dino', coming from the same crude that all conventional 'dinos' come from. Even though their base stocks closely approach the performance of PAO synthetics, they still contain trace elements, and are still susceptible to the effects of temperature extremes that full synthetics are almost immune to. By the way, Castrol does not make their own oil. They never have. They don't even own a single refinery. Never have. They simply buy their base stocks from one of the commercial suppliers (Coastal-Unilube is one), buy a custom-blended additive package from an additive supplier, and have a bottler package and label it all for them. That doesn't mean that it isn't any good. It is very good. But in repeated testing, the Castrol products exhibit a wide variance in performance, the results of getting their products from many different suppliers. 'Syntec' may be good, even excellent oil...but it sure ain't synthetic! "