As I've suggested in some of my previous posts, I believe that the tire pressures on the door sill are those determined primarily by the MB legal staff rather than their engineers and test drivers. The low front pressure is designed to induce understeer (plowing, "tight" vs, "loose") and not necessarily to minimize tire wear or provide neutral handling.
Think about the weight distribution of the SLK -- the front carries more weight and the front tires must do a lot of work to turn the car. I'd run at least 34 psi in the front.
If you run 35 in the rear, I'd keep a close eye on tire wear in the center of the tread 'cause I'd bet that this is too high for as light as the rear of the car is. Also, if you do a lot of high-speed driving on the Autobahn or Interstate, expect more wear in the center of the tire as the centripetal force expands the tire in the center of the tread.
I run 34 psi (cold) all up front and another 2 psi up front for aggressive driving with a lot of turns such as on a road course racetrack or autocross. Seems to me that 32-34 would be best in the rear.
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