I had an opportunity to work with Agency Power here in Gilbert to test out their 2011 Mustang GT Exhaust. I came from the sport compact cars so I already had some background information on them. They are kind of new to the domestic cars and were anxious to fit their newly designed system on my 2011 Brembo GT car.
Overall, this system is great. The 4 inch tips and 3 inch tubing really stands out. The sound is very aggressive and perfect for us V8 loving guys.
Inside the car, it is louder than stock but not so much so that it becomes annoying. I can easily hear my radio with only 3-4 "bars" of volume or talk to my passenger without issue.
Agency Power decided to go with a larger 3" piping to allow for the most flow. Since I plan on doing some kind of forced induction, this feature was a big plus. The seat of my pants feel is great. The throttle is crisp and acceleration is strong.
I have heard the Flowmasters and Borla systems in person and I think this Agency Power cat back system is better. I am truly happy with the exhaust in both fit/finish as well as sound.
I was talking to the owner of Agency Power and he informed me they are looking to sponsor some other 2011 Mustang GT's. I don't have all the details, but I can provide you with contact info if you are interested. The below photos are of my car with their system from their site.
EDIT: I will try to get some custom video this weekend on my Droid phone. Hopefully it will do the sound justice!
2011 Mustang GT - White - 3.73 Rear End - Brembo Brakes - Spoiler Delete and Stripe Delete -- Built 6/10 Picked Up July 24, 2010 | Mods: Agency Power Catback Exhaust, H&R Springs, Work Wheels Gnosis GS1 Brushed Center & Bronze Lip
1968 Mustang - 302 - C4 - Work in Progress