I've just (as in today!) gone from standard 3.6 Carrera with PSE to TopGear 200 cell X-pipe cats and the valves boxes. It was pretty fruity with the PSE but now it's treading the limits of antisocial. I'm sure these cars are louder than you think when you're in them too. Oddly the part I'm most impressed with is how little it has changed with the valves closed. There's a tiny bit more bass than previously but that's about it.