I have a 4" Heartthrob Cat-back exhaust and love it. I wen't with it after I saw a Gearz (. . . I think) episode where they were talking about quick mods to ecoboosts (you can find it on youtube). It does make it a little louder inside the cab, but I've gotten use to it and barely notice it when the radio is on. It is much meatier sounding outside the cab, but that's what I was going for - I like the meatier sound. You can also really hear the turbos spooling - which I think is cool. Haven't really noticed any performance increase, but wasn't expecting much with just an exhaust upgrade.
Cheers.
Cheers.