Now, as for the second part of the title above, we're referring to the fact that these toys had left their factory condition behind. To be more precise, both had been gifted with tunes.
As such, the twin-turbo 4.0-liter V8 heart of the Afflaterbach machine had jumped from 585 to around 700 ponies (yes, we're taking about the power at the crank here, which is the value the automakers use).
When it came to the twin-turbo 4.4-liter V8 occupying the engine compartment of the Bavarian tool, this had been taken from 600 to 725 ponies.
Of course, the output of a tuner car can't be fully trusted until it is put to the test in the real world, which is precisely what the drivers of these velocity monsters did.
Thanks to the piece of footage at the bottom of the page, which showcases the drag race, you'll notice that the driver of the M6 takes off before the GT R.
First of all, with this being a half-mile battle, the element that determines the winner is the trap speed, so the start gap between the two isn't relevant.
Secondly, as the YouTube label behind the video explains in the comments section, the driver of the BMW simply had a better reaction time than that of the Mercedes-AMG, so there was no sneakiness involved.