There has been discussions on this forum whether there is a different (more aggresive) sound from the pipes on the M-Sport or not.
Well, right now I read the option list from the Norwegian importer. Under "Option 337 M-Sport package" it's stated: "650i / 650i X-drive: Adjusted exhaust sound".
Since I haven't seen this information on the forum so far, I just wanted to end the discussion