Ethanol is an Oxygenator so ideally you need to tune your car to get the full benfits of it.
As it burns it creates oxygen (good thing) thus allowing you to add more fuel to create more power. Generally your AF Ratio will will be leaner by about 1 whole point.
ie if your AF ratio is 12.5:1 on normal 98 and you then run E98 your AF Ratio will lean out to about 13.5:1 so you need to enrichen it to make up for the oxygen created during the combustion process. E98 when tuned correctly will also allow about 3 or 4 degrees of further advanced timing so it is definately a good thing in performance engines but will produce the results when tuned on it.
Street Commodores made an extra 30 KW at the wheels on a Tuned Clubsport by using ethanol based premium. The car was already making 230KW at the wheels using LS1 edit software and breathing mods then run on E98 and retuned the Fuel mixtures and ignition advance for a healthy gain.
I delivered 200 liters of E85 (85%ethanol 15% PULP) to a business in Sydney the other day to convert there drag car to run on it. Currently runs 8s on Methanol.....