I have a Gintani X-Pipe with HFC and the stock rear section. LOVE IT!
The car purs almost like stock around the streets with just a hint of a more sinister nature in the growl, but sounds like a freakin F1 car when you hit WOT. I love it...and you cannot complain about the power boost, especially in the mid range torque. Daily drivability and moderate sound levels were very important to me...hence, this was a perfect solution. And my fiance has never complained about the sound, so +2!
2010 e90 M3