On the fuel I have posted it one of the forums not sure which but.. BMW recommends 90 ron as a minimum I think..
Spikey: You can find out the RoN amounts for Shell or BP at their website. For BP its branded as BP Ultimate and Shell is VPower. I certain these two are 98 RON. I'm a big fan of BP as I saw some stats online before that it offers one of the best fuels. I'm sure it doesnt really matter at the end of the day.
Basically the higher the RON value the cleaner the ignition burn. I have tried this and you really want this cleaner burn and combustion of the engine. You will see a lot of threads that Americans find residue on their exhaust (they have a lower RON range, their highest grade could have been 95 and lowest being in the 80's). This is what is left from the burn. Basically this residue in the engine can cause engine knocking.. which is bad for the engine.
David: Similar to you my dealer filled the tank up with RON95 which is of course cheaper cost for them. I ran it empty and toped it up 98 straight away..definitely felt better acceleration after swapping the fuel.