While it's fine to have an opinion on the merits of castor/synthetics based on experience, sometimes it can help to get an unbiased view on the technical side of things. If you read post #2 in the following link you'll find an article written by the Senior Research Engineer of an oil company who just happened to be a modeller as well.
http://www.clstunt.com/htdocs/dcforu...mID1/7221.html

As for how the bottom end of a 4 stroke gets lubricated, I have sincere doubts that blowby is the agent for transferring oil. As someone pointed out, blowby means loss of power and any noticeable amount would be seen or felt streaming out of the breather nipple. To the best of my knowledge, all 4 strokes have rings and this is what I believe transfers the oil from the liner down to the crankcase. The rings act as oil scrapers much the same as the bottom ring does in car engines. In particular this would happen on the power stroke when combustion pressure gets behind the ring to force it harder against the liner. Using rings as scrapers would give a more consistent (and controllable) flow of oil than blowby over the life of the engine. Just my opinion