This week’s tank of gas is 89 octane. The engine noise is very acceptable, not as good as 93 octane, but dramatically quieter than 87.
I would recommend using a minimum 89 octane for the Clarity. I will probably go to 91 myself. It is interesting that Honda’s recommendation is 87 or higher.
The statement about ethanol content suggests using a different brand or gas station, if there are undesirable operating symptoms. I have used gas from Florida to Vermont, and out to Wisconsin, with no change in operating symptoms until I changed octane.
Seems like the extra noise on 87 octane must be damaging some components, even if it is just the exhaust system. It will be interesting if owners start having problems that could be tied back to 87 octane operation. I have burned over 1200 gallons of gas, so I am concerned about the condition of my systems.