I just installed a custom 40 series Flowmaster setup with magnaflow X-pipe copying Quik LS's setup. You can view the thread on here labeled 'Custom Exhaust'. All in all it cost me about $700 but the labor shop charged me up the a**. $415 for tubing and labor!!! And they didn't even do it right! I have to get the tips re-adjusted before I post pics, as of now they hang down a bit too far. The sound is incredible, at WOT it sounds like 5.0 'stang! The HP gain is very apparent. The interior resonance is not nearly as bad as I might have thought. I'd recommend it, then again, I've never heard the Magnaflow or the Borla exhaust kits on an LS. Hopefully I will this weekend when I meet up with a few other LS owners on this website.