far less if not none...
im pretty sure some racing fuels use ethanol.
here... like i was trying to say it just lessens the risk of knocking (higher RON) so that means u can tune your engine more to gain more power BUT higher octane fuels wont give u more power alone
http://en.wikipedia.org/wiki/Octane_rating
so unless your car is tuned for 100RON your wasting your time buying it based on "performance gains", however if your car is tuned for 98 then this will mean you will be quite safe from knocking.