I have 2 sparks, each with about 50 hours on them. I always used 87 up until they were about 25 hours. Since then I have tried a few tanks with 93 octane to see if I noticed a difference. I have gone back and forth. They currently both have 93 in them this very moment. Thinking of trying a higher octane (via an additive). They are stock except one of them has the tech 109hp tune. I have tried 10% ethanol and no ethanol with 87, 91, and 93 octane. I always use a stabilizer additive too. I don't notice a difference with any of the octane or ethanol levels. I have even tried 3 consecutive tanks with each and only fill up when the low fuel alarm goes off to eliminate any chance of dilution. Bummer.
Anyone else have different results?