A Quetico Outfitter, who used Mercury Outboards, told me a story a number of years back about a test Mercury did, with their outboards.hmmm? 93 octane?
Really? it runs on 87 just fine, and I don't hear any knocking going on.
oh well, the local gas pump only serves up 93 pure gas anyway....
but while down on vacation in Florida and Savannah, GA it declared it was thirsty and E-10 was all I could find.