I have a 2004 919. After riding 6,000 km I installed Sato Racing titanium slip-ons. They look great and they have a nicer sound at idle, but they are a bit loud for riding especially for the passenger. They don´t add much power for all the noise they make. You´ll hear a lot of similar comments for most exhaust systems. Mostly, they are for the looks and the noise. However, since I have them now, I intend to get a PowerCommander III. Combined, there may be a noticable difference in power.