I have Flowmaster 40's. I know they're loud, expecially if you floor it. Last night Wes and I were in a rush to find a part and so while we were driving, wes was calling around to find out who was open and who had the part. While he was on the phone, he tried to turn down the radio... which wasn't even on, before he realized it was the exhaust that was making the background noise.
My Advice? I'd say try some Flowmaster 50 Delta series. The Deltas are supposed to give the same tones, but be a littler quieter. If you're concerned with noise on the inside of the cabin and not so much on the outside, another good idea would be to pull your carpet and put down some dynamat or similar material under it. Along with the exhaust, it would also help keep out road noise and keep in music or whatever else you use your stereo for.
-Dan