Flowmaster 40 without deltaflow is the most aggressive. With deltaflow it decreases some interior resonance. It is all up to you. If you want something nice and loud and you dont mind the inside drone, then the FM40 is for you, if not go with a FM50 series, or dynomax. I am running a Thrush cherry bomb glasspack with dual inlet single outlet and I love it! It has the perfect sound and little to no resonance inside. I paid like 50 bucks for it. Part number is 24218. This glasspack is dual inlet, single outlet. If you go with dual outlet setup, its going to cost alot more, since they have to fabricate the tubes for the driverside plus the chrome tips, and labor you might be looking at close to $350-$400 bucks out the door, while just bolting up the glasspack or muffler and keeping stock pipes is about 1 hr labor which cost me $65.00 out the door.