It's so much hassle at the moment, Optimax is about as best as you can get but check your jetting as it's density can effect the mixture. If you run premix it's the same sort of deal. Mix the oil with the fuel before the carb and it leans the fuel / air mix off a bit. I feed all bikes / cars nothing but optimax - works well especially if you are running a bit of extra ignition advance.
Avgas is readily available for high compressing motors and nice and cheap if you can find a supplier who will sell it to you without the tax
just don't forget to consider some phosphour bronse inserts to the squishies.... or there could be tears before bedtime.. _________________
These aren't the droids you're looking for.