Just had my stock muffler replaced with some pipe. I was amazed at how quiet it still is!! I have to turn off the radio on the highway to even tell there was a change. Just a slight difference at idle, and a little more turbo whistle when I let off the pedal. I would assume its pretty close to a 4in cat back exhaust performancewise, just a lot cheaper. All in all I'm pretty happy with the price/performance value of ditching the muffler.