My GS455 has stock manifolds followed by the full stainless 2 1/2 inch Magna Flow exhaust all the way back to the rear bumper with an X pipe about 1/2 way back. While, yes, it does reduce that deep musclecar sound it has been found in testing to increase performance some. And it sure is nice being able to listen to my favorite music and talk hands free on my new AM/FM Stereo, Bluetooth radio conversion. No drone either.
I should probably close this thread as I've decided to stay with stock iron manifolds for my next build.
yes there is a performance gain to be had with an x pipe however it isn’t major and like Ethan said there is nothing like true duals for sound.