It completely depends on where you live, the engine in question, and the operating conditions at the time. The old schoollittle guys usuallyhave fragile internals and in most cases today, replacement parts or service is non-existant so be guided by that.
The castor content needs generallyto behigher inhot weather than in cold, the nitro ratio can change alsoto suit.
That said, back before synthetic oils, we ran the Cox fuel out of the can here locally and we had more blown (fouled) plugs here in theSummer when it got above acertain temp/humidity level than at any other time. Today, I would drop the castor off atad andrun slightly more synthetic.
Best is mix your own. In most cases, you can have it mixed for you by one of the custom blend dudes.
Iused to run some of my OK Cubs on FAI fuel- in cool weather- but performance wasn't great, even for a Cub.