When the Crossfire first came out, I believe Motor Trend did a comparison road test of the SLK 320 vs the Crossfire. Of course these were NA cars.
Even though the SLK had 17" wheels, the tires must have been the same diameter as the XF's 19's, because they were both turning the same RPM's at the same speeds.
But the Mercedes had a more narrow tire, so it had less rotating mass to deal with, thus it ran the 1/4 mile, 2 or 3/10's faster than the Crossfire.
Now I would think for this very same reason, these tires would make an AMG equiped SLK slower in the 1/4 than a SRT6, since we all know how important those wide 19's are for a good 60' time.
With the exception of a more comfortable "luxury" ride, the Crossfire soundly trounced the SLK in every other catagory. I just wish I could find the magazine to be more specific.