Ethanol is awesome when it comes to knock resistance because it is much slower burning than gasoline is with all other parameters being equal. Where it bites is that it requires better seals than gasoline, and it has lower energy density, which means you need higher flow fuel pumps, tubing, filters, and injectors to make the same power.

Do that, though, and you can run a turbocharged engine at much higher levels of boost and create much more power than you would be able to do with anything short of race gas or even more exotic and dangerous fuels.