Castor is a fine oil -- but not necessarily any better than the newer alternatives, particularly when it comes to issues of film-strength in high-pressure areas that operate at lower than cylinder-head temperatures (ie: the big-end/crankpin interface).

You'd be rather shocked at the low levels of lube I've been playing with (on disposable engines). The better synths are bloody impressive and I'll gladly run them at ratios much lower than would be even remotely sensible with castor.

Feel the force :-)