Does the slk have a different diameter tire or just a smaller rim? Keep in mind one can up or down a rim size, but still keep the same overall diameter, just the tire will have different side wall heights. I forget the formula but I remember that hearing that losing a pound in unsprungs weight was like losing several pounds in the car. I thought it was like 1 to 5. Maybe some one could confirm that ratio. I would like to keep stock sizes rims, while going with a lighter rim but I have not found a rim that would make a difference.