One of my best friends owns an SLK 32 AMG (the version before the 55) and while it is stupid fast and has 350 HP, it has a totally different feel when compared to the Boxster. Riding in the Boxster really gives you the feel of riding in a sports car; the SLK feels more like riding in a sedan.
And like Jeannot pointed out, I'm always giving him a hard time about my car being faster because his limited. He always replies about wanted to drag race. All in all, its still a very nice car, however after getting to know his SLK I'll still stick with my Boxster.