Stock vs stock your gona lose. The slk has all that power plus a 7 speed tranny which always manages to find the sweet spot of that engine(which is most of the rev range like our cars)
I used to own a C55, same engine but 5 speed auto instead. Raced a few 335s that were stock and pulled about 2 car lengths.
Put a jb3 in your car and you'll be pulling