What is your fuel/oil ratio for full synthetic 2T

Hi Fellow Addicts

I am moving to a full synthetic oil for my grubbee 66cc superratt.
im currently running 35:1 on mineral oil. Engine has done around 600 miles, so it has run in nicely. The oil is Castrol tts 2t full synthetic.
Please any advice on weather i can lean it out to 40:1 ?? and any other preperations i should look into. Also fuel - what octaine is best i run 98 is it nessesary or am i waisting my money?
What are you running??

cheers

cheers for your replies.....im paying around $1.30/L for 98 octaine on a good day that goes up to $1.60 on weeekends i know its not bad as in euro its $2.90