Just to put this debate in perspective;
The cars as standard are likely designed to run on anything as low as 90 RON petrol... thats the standard in Japan and many places around the world. Premium fuels (most of europe, including UK) average around 92-95 RON and anything higher is seen as super premium...
http://en.wikipedia.org/wiki/Octane_rating
Im NOT disputing that the cars ECU can adapt its timing to suit the fuel - it is certainly well within the realms of modern ECU's to do this, OR that there is no performance gain from using 99 RON fuel but whatever fuel you use it is worth remembering that the standard engines will still run fine on 90 RON fuel.
How much is hype driven by marketing and how much your cars performance is effected can be a very personal opinion - Real world performance is something that is very hard to quantify as there are so many variables.
Obviously this is purely for the standard engine... once you start to modify it, then that opens up all kinds of avenues and the answers really depend on how good the tuner was, how much they understand and how specialized you asked them to be...
What I'm trying to say is that this debate is useless as the engine output is completely subjective to the individual car and conditions its being run in...