Magnaflow is the best quality muffler/exhaust you can buy, in GENERAL. I dont know about the exact specifics for the 7gc; but many professional racers swear by magnaflow. If you check on their website, there's a reason why many of the exhausts seem.. weird looking. Its cus they're not geared towards ricers with a billion fireball clones- they're doing it for Performance and they achieve.
As for sound, magnaflows sound awesome- better than a TRD
exhaust IMHO. Until you actually open up the throttle, the magnaflow is actually REALLY quiet- so it's totally safe for street driving by cops and doesn't need a silencer. Open her up, and it's a nice deep non ricy roar.