Not really, both are high pressure supercharged engines that, from the factory, share the same exhaust manifolds as their normally aspirated versions. Sure you can't expect the same amount of HP gain but there most definitely should be something there to gain. Problem is we don't have the room those sedans have to build a quality header with a nice merge style collector.

I recall a member (AMGrasol?) built some long tubes for his SLK and he did that in the same fashion as the old Ford guys when they stuffed big blocks into the mustangs by routing the pipes towards the front and then back to the collector on some of the primaries. I don't remember him ever data-logging for a tune either so I feel that area is still largely uptapped for now.