Treven,
Most motor oils will give there EP rateing in there API or product sheet as its quite common for motor oils to be used in transmissions/differentials were the EP rateing is an important design factor.
I noted above that castor is used in gokarts and competion 2st's eg motorcycles , Klotz sells most of its benol to these users- modelers are only a small fry user. Go karters and other 2 st users have found that nothing gives protection like castor, but it does comand higher maintainance in the form of varnish removal- but if theres varnish then there would have been high wear rates with an alternative lube oil.
Stewart