Ethanol is crap.... It has less energy then none ethanol and you will use more in the long run then with standard gas. It also eats rubber and will loosen rust that has built up in the tank over the years. This will cause fuel filter,carb jets and bowl to fill with rust.

Higher octane is not needed for an engine with 8.5:1 or lower compression with out boost, and no you will not get better mileage running 91 over 87 on a none computer controlled engine (Timing) as the engines now a days will increase timing till it knocks then back off the timing. On a higher compression engine or boosted you will need to run a higher octane so they don't ping under load. My 2002 F-150 I use 87 octane as the engine is only 8.5:1 compression but the D50 is running 11:1 and the bastard pings like a mother unless I run 93.

If you run 91 you can advance your timing up before it pings and it might help with the MPG and give you a little extra power.