Take it from somebody who has the American Thunder...there is no normal conversation in my car, there is no listening to the radio unless it's loud enough that everyone else on the highway can here it too. The rest of my exhaust is equal length shorties and an offroad H-pipe. Some have said that my car is exceptionally loud because of the higher compression ratio. Don't know if there's any truth to that or not.
I called Flowmaster, after I made my purchase, and they told me that the 3 chamber mufflers are designed to sound the same from behind the car as the 2 chambers. The only difference is supposed to be the noise level in the car is lower with 3 chambers. Call them yourself and see what they have to say.
I'll definitely be getting the ForceII next time around.
BTW, I don't romp on it in town anymore because I got tired of being stopped by the local cops who have nothing better to do than enforce sound ordinance codes. Probably ok for normal driving. But if you're going to drive normal all the time, you might try a saturn or a neon