I thought all gasoline was required to have ethanol in it. I was not aware that 91 octane (mid grade?) was not required to have it. Is 91 octane ethanol free everywhere? If it is, then I am definitely changing to it. The flame propagation time of the slightly higher octane would be insignificant to engine timing.
I left a tiny amount of fuel in my mower over the past winter and it gummed up everything. You know that bad-gas smell and I knew it for several hours as I cleaned the fuel system out. I will never forget to drain my tank completely, I will never forget to drain my tank completely, I will never forget to drain my tank completely...
I know that it messes up boats because it absorbs moisture rapidly, gets stale faster, is detrimental to fuel system components, and I cannot leave it in my standby generator for the season even if it is treated with Stabil because it might not start.