Lower octane will give you higher MPG.

The higher octane gas ( these days ) is being cut with ethanol to give the higher octane number... which will give lower MPG... but at the same time it is cleaner burning, and cleaner for your car.

So it's back to a case of pay now, or pay later.

It should be noted that OCTANE is NOT an ingredient. It is only a NUMBER. The number does not tell you what is in the gas. The number tells you how the gas behaves. Ethanol contains zero octane molecules, but has an octane rating of 110. E85 has an octane rating of 105.