Different engines in different cars may be able to adjust the ECU to take advantage of higher Ron fuels but if VW say the MK7 GTi is optimised for 95 then that implies that the ECU does not adapt to higher Ron fuels.
Historically, at least this is not the case. ECU would adjust to protect the engine from lower grade fuels than it was optimised for, there was more than one way this was achieved but typically one or more knock sensors were fitted and if/when knock (detonation) was detected the timing was progressively retarded until it stopped. After a time the ignition was advanced either to the "optimum" or until knock was detected again.
So, in both my Integra Type-Rs, my S2000, my 911 etc. which were optimised for 98 it made an appreciable difference to performance and economy if you have to fill up with a lower grade, you lose, I would estimate close to 10% as the timing adjustments are fairly crude and non-optimal. Modern ECUs may well be better at this but I am not aware that they adjust upwards for better fuel...
So, there really is not benefit to running V-Power in a car optimised for normal from a power perspective, long or short term. The additional cost 5p per litre (give or take)... if you do say 20K miles per year, you'll use over 2000 litres to do that and the additional cost will be over £100 for no benefit, except a mis-placed peace of mind... I suppose it is not too bad but I'd rather have the money...
