Same here in MI. This was mid summer, 93 was 2.89 and 91 w/o ethanol was 3.19. My Cruze is tuned for 87 to 91 and I was trying to see if 91 with no ethanol would give me better gas mileage. The answer is no and if it did it wasn't worth paying nearly a dollar more a gallon than running 87.
To OP, I accidentally put 91 octane in my GN. I put about a half of tank, then mixed the with 93. I seen no knock at 18psi, not spraying alky.
