If I may, let me put some myths to rest. Ethanol fuels will not harm your engine, nor will they harm your carburetors or fuel tanks... when constantly in use. If you allow the fuel to sit for an extended period of time, it starts to soak in water. The moisture, along with oxygen is what causes the corrosion, not the fuel.
Now, about the high octane fuels. Octane ratings describe the fuel's resistance to knock. Knock is when the fuel mixture ignites in such a manner to make an explosion instead of combustion. Think of combustion as a controlled release of the fuel's energy, explosion being a complete release all at once. So in general terms, the higher the octane, the slower the fuel burns. This is necessary in an engine that exerts a lot of energy on the air/fuel mixture, such as a high compression or forced induction engine.
So what foes all that mean? Essentially, if you use too high of an octane fuel in an engine that doesn't actually REQUIRE it, it results in an incomplete burn and you will waste gas money because you are not getting all the energy you can out of the fuel before it leaves the engine.
Unless the compression ratio is high or it's forced induction, I'm running 87.