I have IMCO Extreme 55506's on my 5-speed 05 GT with a Mac Cold Air Intake and they sound BAADDD... What I really like about the system is that the exhaust doesn't pop/crack or tumble during deceleration. The system sounds more like the older 5.0/302's of the earlier Stangs. Mod motors seem to be prone to popping on deceleration around 2000-1800 RPM, especially with off-road H pipes and after market mufflers.
If you had tried the damaged set prior to cancelling the order, I believe you would have waited for the replacement set to arrive... Go to this website for a sound clip on the 05 Mustang... grabthepower.com - click on SOUNDS at the top - choose FORD then MUSTANG - then choose 2005 Auto or Manual.
Here is a pic of mine installed.... Bobby
Arrived Damaged.....IMCO waited a couple of days to ship new ones...I canceled the order. I am now trying to decide between Magnaflow & JBA.