I will give it my best shot: The X6 ///M has a Dr. Jackal & Mr. Hyde persona.
Driving off is all quiet and composed, tap the throttle and the free revving nature of the Twin Turbo V8 is worlds apart from the 50i. This car has a totally different temper, sound and 'soul'. The words ///M immediately makes sense and the Magic they make! If our own Martin did not know about the X6 M or haven't heard nor read about it, even he - the master of drive train engineering on GCF could IMO be convinced that this V8 Twin Turbo was a NA engine! Because of it's free revving nature.
Push the M button and plant your foot....OMG! The sound emitted by the 4 tailpipes is DUCATI Superbike (sorry BMW Motorrad) But that is the truth and noting but the truth. The car is also more planted to the road and the lack of wind noise compared to the 50i instantly evident, so the 'body kit' was engineered on the track. The power surge is instant and intimidating so much so that the 50i feels like grandma's car...
In the end I am convinced that after owning a V8 TT 50i and now the -
V8 TT ///M even Betty Swollocks would give BMW M the thumbs up!
One thing is the lack of the sense of speed - SAV!? Yes! It's higher center of gravity steals the 'ass to the tar' experience...unfortunately.
http://www.germancarforum.com/my-car-owner-galleries/37436-dream-come-true-my-new-bmw-x6-m-3.html