The Castrol also expands at high temps, as the molecules "unwind". Therefore in a Cossie (which doesn't like being over-filled), you will "appear" to get high oil consumption if you fill it up to the top level, as when it gets hot, it will go over the level and then get blown out the breather system. When it then cools, you have "used" a lot more than normal...
Silkolene for me, as in Rod's car (200mph) it showed NO chemical breakdown at all after a high speed run (where the same could not have been said of the others, which had sheared and lost a lot of their protective properties
).