I have the same exact set up as you, 89coupeex2. I like it, but I want it a little meaner sounding. My friend owns a muffler joint and he said pro dumps are indeed the way to go. Getting mine put on next week.
The dynomax ultra-flows have a really mean sound, pretty quiet at idle though. i think 3" ultraflow and dumps would sound pretty sweet and its a break from the usual mustang tone.