My car runs incredibly rich, so just for s**t and giggles, I mixed my fuel with metho (the 99% ethanol stuff) to lean it out a bit. No deterioration of anything, nothing broke, and basically the car drove much better, but of course YMMV as my car does run rich, and I put enough of it in to lean things out but no more, hence a much better running car, with more power.

A good idea would be to buy a cheap Wideband Oxy controller like WBO2 and fill the tank with increasing amounts of alch until you get to the point where it could be unsafe AFR wise, though some efi pumps die with high % mixes, and ethanol is an excellent solvent so will disolve a lot of things (rubber hoses, certain plastic fuel tanks). You will find that as you increase the amount of alcohol the engine runs cooler, and you can add more timing (if you don't have coil packs) both of which will get you more power, the big downside is that ethanol attracts water, so you can't leave a high % mix in the tank unless its a sealed system (this is what they do on flexible fuel vehicles in the states)

Oh for pre mixed 100 octane here in perth, oh well, for the time being I'll just do it myself