I'll probably get slammed for this but this discussion seems to be pretty standard whether it's on this board, the Mercedes board or on the Cadillac forums.
I think bottom line is is that whether your using BMW recommended, Mobil 1, Redline or any other manufacturer recommended high quality top of the line synthetic oil then you can't go wrong.
I mean has anyone ever heard of early engine failure, or excessive oil consumption or engines that couldn't go a couple hundred thousand miles because of one of the top of the line oils?
I too think that my engine sounds quieter and runs smoother after an oil change, but then again I think my car goes faster and runs better after I wash and wax it too.
These discussions are great and interesting, but I just think there is no proof that one of the high end oils is better for your car than another. If there was then we'd all be using the "best one".
As long as you use a recommended product go with the one you feel best with.