Since the early days of ownership with everything very standard, including the engine pinking at about 4000rpm that the restrictive standard exhaust did, I have run mostly with the highest octane fuel I could get. It's a little more expensive but in the shape of things for the general mileage, not much in an effort to reduce the harmful pinking. Since going Stage 1 G56 and an unlocked, rolling road optimised ECU, the pinking has gone at all rpm's and doesn't even happen on those occasions when I have to use 95 octane fuel, so it's not the fuel that causes detonation. Your Brooklands system should be similar to a Stage 1 exhaust, so I think it will run OK on UK standard 95 RON fuel but maybe better of 99 but that may be just a perceived performance improvement, as you say. It's not a turbo charged 150bhp per litre engine, so that little bit extra with the fuel shouldn't make the difference.....but I still use the 99 RON stuff when I can.
