NaturalFlavor +3 because that axle back used to be on my P5.
To my ear, the sound of the mazdaspeed muffler is slightly lower in tone (bass) and more audible at an idle. Whereas, the racing beat cat back is silent at idle and mild sounding on a mellow acceleration but then nice and throaty when you step on it. The mazdaspeed muffler will start to get loud or drone, in my opinion, at 70mph+ freeway cruising speeds. I like my racing beat cat back for how much more quite it is at freeway cruising speeds because it makes it easy to listen to podcasts and music (at a reasonable volume).
No doubt about how the mazdaspeed muffler has a sporty note. A friend of mine who owns a show going '69 Chevelle was astounded by the sound of the mazdaspeed muffler. He said it was one of the best sounding exhausts, too.