I personally have a Magnaflow dual 2.5" in single 3" out on my 5.0 Explorer. Its dumped right after the muffler. You get a nice, deep tone at idle and up to about 1800 - 2000 RPM. Above that, its just a mild rumble, nothing too loud (with the stereo up I can't even hear it). The only time outside that range its noticeable is when you're really on it.
Of course, there's probably even less noise when its not dumped right under the rear seats in the X, so if you route it out the back or the side, it would reduce even more cabin noises. All in all I love the sound and performance I get out of it, although I am planning on rerouting it out the side so that I don't get as much resonance at idle (from reflections back off the road).