O.K, lets take the USA, in many, in fact most places 91 Octane is the highest you can get and 93 seems to be the highest available anywhere. Now because the Americans use a slightly different way to calculate their Octane rating (they would wouldn't they ) which means that 91 in the US is the same as 94/95 here and 93 works out to 97/98. The simple way to work out octane ratings is to use reference benchmark materials, for example 100 Octane would be 100% Iso-Octane, 95 Octane would be 95% Iso-Octane and 5% Hexane, simple really. Anyway, I digress, to get higher octane ratings used to be easy and cost effective, you would just add TEL , Tetra Ethyl Lead and this boosted the octane rating as TEL is a very good anti knock agent. However, the law changed and TEL was considered to be too dangerous to human health so Oil companies had to come up with something else. I worked for a company that came up with a solution that not only increased the Octane rating but helped to make the engine run a tiny bit better. Big profits involved here for what are quite small amounts of additives. Companies that we sold the additive packages to, Shell, Esso, Mobile,etc also make big money from selling these on to you and me. The Americans just aren't interested in paying more for fuel, they think $2.50 is outrageous, so very little of the Octane booster is sold over there.
So, is it worth the extra cash to put the super dooper fuel in? Well, you can't get it in The States and the majority of Zed owners seem happy with 94/95 Octane fuel. From some of the engine tests run with the booster, engine life was certainly extended but who wants to keep their car for 180k miles? My advice would be if you are running on the track, put it in, for everyday use, don't bother, you're just contributing to the already vast coffers of the Oil companies.
Here's a typical American pump BTW.
Pete