Different octane rating for petrol

The article in the Life! section of yesterday's Sunday Times should convince most car owners that 95 octane petrol is more than sufficient for their cars. I still do not understand why is it that many who pump 98 octane claim that their car performs 'better' as compared to 95 and 92. I tried all three grades of petrol on my previous Civic and I got the best fuel efficiency on 92 octane. If I were to be a little heavy-footed, 95 works best. My current Altis runs extremely well on 95 and since I already have the broquet fuel charger installed, technically speaking, I can use 92 octane. Perhaps I should switch over and end up saving 3c per litre?