Horizion advocates 30% Heli fuel for the oil content and the fact that the extra nitro improves idle and accelaration in the Saitos.
All other 4 stroke manufactures advocate regular 2 stroke glow fuel. That's what they where all designed to use. 15% Nitro helps idle and accelaration.
A small amount of caster in the fuel is good, say 5% to help with film strength. But to much and it can build up on the exhaust valve if you run the engine a little to hot.
If you read the book by Clearance Lee of RCModeler titled the RC 4-Stroke Engine, it can help with a lot of questions. [&:]