Zahanma is spot-on.

Many members here are putting down close to 350 RWHP with the Needswings parts and a tune...

That number would be WELL above the ~400 BHP which is what the SLK is the video is claiming to have.

I think it's interesting that the SLK gets a healthy jump on the M3 and keeps that distance until well north of 130mph. In other words, many SRT-6s on this forum would walk the new M3. The video tells the story; torque is your buddy. Honestly I think the SLK in the vid fell off due to IATs...

Note that the SLK in the video also has the Kleemann differential... I know that's a point of interest for many owners on here.