I will usually run E-0 87 or 88 octane in general. Keep in mind around here regular fuel is 85 octane. I will run 91 if towing or usually on a road trip I'll top off with 91 and run 91 for the trip. Also in the hottest part of the summer I will usually run 91. Most of the time I just run the mid grade, which is 87/88 octane. I haven't noticed any difference really with mid or premium or non ethanol. Just seems like a good idea to run the 91 in some circumstances.