I noted that there were several posts in this forum about tall people driving the SLK350. I am 6'6" tall and have very long legs. The dealer looked at me when I ordered the car and said "remind me when the car gets here to have the seat adjusted for you". I asked what that meant, and he said that "all MB cars have some extra travel in the seat tracks" and they would move this "back" for me.
I got the car and fit very well. The dealer said that they had "adjusted" the seat for me.
So if you want, I would suggest asking the dealer if he could please set the seat tracks back if you want a bit more leg room.
I do have to be careful though, as the seat does physically touch the back of the car and the seat back can literally be pushed too far. So, I am careful as I can probably break the seat by pushing it too far back.
Good point about pushing the seat to far back. I'm 6'4" with big freaky long legs and have to be careful when setting the seat incase it pushes too far.
That said, I was surprised how much room there is in the SLK for us tall people, although when you set the steering wheel up you can't see anything on the dashboard (except for speed in km/h - which is useless in the UK).