[84LX89GT]

I have Flowtech Stinger mufflers on my GT and they are quiter with an offroad-H pipe than brand new mustangs bone stock. They sound really deep and throaty when you get on the pedal, but at the same time it's not "loud". They're basically just a regular "turbo" muffler design with 3 perforated cores, and they're fairly heavy for a muffler, but i can see why because there's quite a bit of sound dampening. The only time people notice the sound of my car is when i'm accelerating or they're standing behind it. I imagine that with catalytic converters, those mufflers would be EXTREMELY quiet. The best part of them is although you hear the 2000rpm drone, you don't FEEL it and it's not loud enough to disrupt a conversation or overcome the radio. I'd recommend this muffler for exactly what you're asking for, it's about as loud as Dynomax Super turbos on a stock 5.0L with stock 4-cat H-pipe.
For someone looking for a ripping, screaming sound these mufflers are definately NOT what they'd be looking for.