Here's my exhaust clip contribution. Installed as my FIRST mod to my 2007 Pony Package 'Stang. I got the Magnaflow cat-back but ordered the GT kit with regular style mufflers (not the magnapacks you get with the V-6 set-up)
Less highway drone (very mild) and more realistic V-8 sound. Also had an X pipe which I should have just added another Y as low end torque did suffer somewhat. About a $1000.00 installed. 3.73 & SCT will help low end...next.
http://www.youtube.com/watch?v=NlUwi4Ew-lQ 