Yea, i have heard the GMPP "Touring" and "Sport" Exhausts for the Cobalt SS, and they are considerably deeper and louder respectively. Very nice for exhaust on a four banger, i prefer the Touring because of the deeper rumble rather then the louder rasp common to four bangers.
I imagine GM will have somthing considerably similar for the Camaro as well.
And i have a 3" single outlet Magnaflow Ultraflow II exhaust on my 305 equipped Caprice, and it yeilds a lovely rumble under idle, and full accel, while being very tolerable at highway speeds. Dual would be very nice, but probably annoying out on the highway at cruising speed.
I won't comprimise when it comes to my Camaro though. It will (most likely) be GM shorty headers and a GMPP Sport Dual Exhaust.