Twin Star, most 2s outboards are not helped by octane > 87. I have lots of experience running and rebuilding outboards and can tell you that, except for high compression racing motors, higher octanes just result in greater deposit formations, which is not desirable at all. I currently run a pair of 175HP E-Tecs offshore, with tons of both high speed and trolling time and run the lowest octane I can find (89 at most local marinas). I also run a number of low HP motors as well. Avgas is not really desirable, but finding zero ethanol fuel will really help. Ethanol, by volume, has way less BTU (and therefor energy) content than gasoline, which is why you see a significant reduction in mpg is vehicles using it. I've found a local marina selling zero ethanol fuel, which is where my boat and models get their fuel.