SLK 55 Sway Bar
Making the front bar stiffer will cause your car to push more (= understeer more). Changing parts or settings on the suspension should be done at a track where you can test the result and tune it to where you want it. AMG did this to the CLK55.
If you want a change in handling characteristics, I would recommend you buy an entire "package" (front & rear sway bars, stiffer springs, plastic fittings instead of rubber, etc) that has been developed and tested with your model car. Just changing one part will not have the effect you desire.
Heman, you may get your desired results by simply going with coil overs (I cannot tell by your last post if you already have PSS9s or not...).



