I have tried the 3 1/2" flowmaster race mufflers,Dynatech splitflows,Hooker Aero chambers and the 6" oval Magna flows. The Flowmasters were the most quiet out of them all but cost 1.5-2mph. I have been the fastest with the Aero chambers and they are not to bad with the noise either.

PRH446
10.084 @ 135.21 mph N/A through chambered mufflers,3300lbs. Stock stroke wedge