Fitted a Brabus chip to mine, not noticed any great performance improvement to be honest, but I guess you would need to conduct scientific tests to establish actual figures. It did seem a lot smoother though after it was fitted. It isn't going to suddenly give V6 performance.
Not sure of the increase to the mercedes but can say that when I fitted a dtuk box to my insignia the difference was huge. In both performance and mpg. Also had the same effect on a previous vectra.