LET, which is now Eurocharged. I went to Chicago more than once for a tune, and we all spent time at the track running side by side as well. No one has de-tuned the motor. Gets delivered, it was a JIT facility, so the motor went straight to the assembly line. There was an AMG video out a few years backs showing a motor being hand built. If you spend any time around the motors, you can see for yourself. Steve had his SlK, did the same build as we do to our XF's...just isn't the same engine room, but many things are the same.
As far as motor trend, automobile, road and track...doing side by side comparisons. It isn't any different than drag racing. NO one lauches exactly the same every time. NO one is going to perform exactly the same each time. So when you see cars within a few thousandths of a second apart, that can very well be driver, not the car...
In fact, I remember taking Matt's stock SRT6 coupe out trying to break the 12's for him and did a 13.1. He had never done this himself, but the car did with a different driver. We could go on and on, but the bottom line was AMG had the motors and Chrysler had the car, and Karmann put it all together....