I'm running the mild steel twin 2.5" XForce on my F6, sounds good enough to me with no drone and for the price I payed ($700 new for complete turbo back) I couldn't say no to it. I still haven't fitted the 4" dump and cat section though, so I'm sure when I do that it will be slightly louder than it is now. If I wanted a loud droning *beep* of thing I would've kept my evo x with it 3.25" titanium turbo back..... Fark that thing was loud when ya booted it and droned like a *beep* on the open road.