I only ever used Tesco Momentum 99/Shell V-power/BP ultimate in my mk2 1.4Tsi sport.
It wont do any harm to run on the higher octane fuels. My car ran very smooth on those fuels.
For me its not about any alledged bhp gains, its about using the fuel additives in the higher Ron fuels to keep the fuel system as clean as possible.
Think of it this way......
You could use ordinary unleaded in your car, but then, if you want to clean out any harmful deposits from the fuel system, you'd have to then buy a fuel additive like Redex or similar to run through your system with a tank of fuel (if using 95Ron all the time)
Worse case is that you may have to get a carbon decoke service like Terraclean done eventually.
Whats the point in spending extra money on Redex to run through a tank??
You may as well just run your car on the good stuff from the off, its not that much more expensive & at least you'll know that your fuel system is kept as healthy as it can be without the need for buying any Redex or risking having to spend extra on a Terraclean service