I've just taken possession of a load of Liqui-Moly Octane booster. I've been trying it out for a couple of weeks and its great. It supposed to boost fuel from 95 to 99 oct. Maybe it does but thats not the point. The car runs a lot better- it also cleans the fuel injection system. I've noticed a significant performance boost.
Motor factors I think will be selling this for about 9 or 10 euros a can (1 full tank of petrol) while i'm doing 2 for 10 euros. It works out a hell of a lot cheaper than sticking 97 octane from a garage into the FTO and its better!
email me offline for more info and my number!