I'm afraid your question is a bit too general and prone to personal preference...
...but generally speaking, high octane fuels are for high compression engines (which most stock bicycle engines are not) & the "best" ratio for a synthetic is whatever the manufacturer of the synthetic oil recommends for that oil
We've ppl runnin' anywhere from 24:1 to 100:1 and all seem to love w/e it is they've got lol
I couldnt even dream of goin to 32:1 I reckon it would be way too leann, not sure if its coz of the higher octane we have here or the two stroke oil being used.
I was using valvalene oil b4, after switching to the castrol the carbon build up has reduced massively.