Aftermarket exhausts...any performance increase?

[panic]

Are aftermarket louder mufflers for M3's any good for performance as well? Has anybody ever prove with a dino sheet an increase in performance after installing one in an M3, what about in a new E92 M3?
Will the ecu 'feel' consider the variation of back pressure to variate the other parameters or eventually a tune is needed? thans/Giu

[panic]

[quote=EvoJay]Depends on which car exactly..e46?

...I was talking generally, but if we want to be more specific, about the E92 M3...i'm waiting the new Eisenmann (race sound) mufflers, i just wanted to know if i'd expect a few ponies on top of the present 420 or will i get only a 'better' sound out of it.