I'm using M&M's, no cats, and those super long mufflers from a MOPAR perf exhaust. Not all that loud actually.
The initial dyno gain was about 37hp, 39ft/lbs tq. N/A car with just K&N, 172'thermostat, 3.55's, and B&G flash.
Thanks to Matt and Mitch for the awesome headers. And they do...