[Madgambler]

I've used Shell Nitro+ for almost all of the 86K miles on my F21 since new and when I decided to give the engine the walnut shell treatment at the dealership a while back they did comment that the amount of carbon build-up was markedly lower than expected. I put that down to the fuel being relatively clean and decent at cleaning, so I'll continue to seek it out in future.

I know the extra octane rating (here in the UK it's labelled as 99 RON) converts into only a small useable horsepower boost on the road but on the odd occasion when I've had to put something else in, even an equivalent higher octane alternative from another UK outlet, it never quite feels the same.