Reformulated Gasoline

Hi all,

I have a 67 Dart GT with a later year 360ci engine (not sure of the year)...here in Milwaukee, like most metro cities, we are limited to only having the reformulated gasoline (with 10% ethanol) for all octane levels.

Would I be better off using a higher octane (92 or 93) or would the regular 87 or 89 mid-grade suffice? Not sure what other options I have.

Thanks.