The Castor vs synthetic "debate" is an interesting one. I too recently go into 4 strokes. I have a Saito .91 that runs great on 10% cool power (100% synthetic). But when it comes to fuel you will get all kinds of advice. Here is what I have come to understand.

Castor oil provides protection at higher temps than synthetic so theoretically the 4 strokes will benefit by having some Castor oil in the mix. In fact the Magnum 4 stroke engines say they should be broken in with a fuel that has Castor in it since the engine will run hotter with 100% synthetic.

There is also a new trend at my flying field, and someone mentioned it here and that is people are starting to add extra synthetic oil (aka Klotz) to their fuel. Not sure how this started or why people feel that more is better. Maybe someone here can address that.

As far as Nitro is concerned, the four strokes don't need very much since their power doesn't come from high RPM but from torque. The 10% should work fine for you 2 stroke unless you are flying something high performance.

Hope this doesn't confuse you to much. Otherwise just fuel them up and go fly. If the engine runs great with what you are using don't feel obligated to change anything.