Stay with the MAC you have, Scott. Drags are a chopper thing, and they have ZERO backpressure, which you motor needs. These little 550's need all the power they can muster....there is no "extra" to give away.
Play around with the baffling to get the sound you want. BBQ grill paint is cheap and works.
Save your dough, keep the wifey happy, and stay put.
Just my .02
~Joe