The best way to compare more/ less power is to look at the lower heating values of the fuels and then compare the stociometry.
Ethanol 28.865 MJ/kg
Octane 44.427 MJ/kg
I've chosen Octane but really the heating value is about the same for C6-C12 hydrocarbons.
Ethanol burns at 9:1 and petrol 14.6:1 so the equivalent heating value of ethanol in replacing petrol is....
28.86x14.6
----------
9
=46.8

So slightly higher than petrol supporting the argument of slightly more power with nothing but fueling mods for a high ethanol blend. You also get more cooling and potentially more air into the engine.