I installed a 40 series Flowmaster on my car to solve the same problem and it works great.
On the inside its alot quieter. When cruising around the interior sound is almost gone except for when the engine is at about 2000 to 2500 RPM, then there's a little sound but its far more bearable then without the muffler. But what I like about it most is that when you get on the gas and rev the engine out, it still has that roar (but more civilized) in the interior that lets the passengers know that this isn't your everyday grocery getter.
On the outside, at idle its a very deep low tone, when cruising its quieter and more muffled, when you get on the gas and rev it out the flowmaster doesn't do much except kill the rasp, take a little of the edge off the sound and add that signature Flowmaster sound.
Installing it though was interesting. I used a 2 1/4" offset/offset configuration with the inlet and outlet on the same side of the case. I had to "adjust" the heat shield a little on the underside of the car in the well where the stock resonator once was. I used a rubber mallet and a piece of 2x4 to enlarge the opening in the heat shield enough to give me about 1/2 inch of clearance all the way around the muffler.
If you are worried about the Flowmaster rusting over time, spend an extra $15 or so and get the stainless steel version.
