i had magnaflows on my GP before with 3.4" intake 3" DP and full exhaust, it wasnt too loud but it did have a nice deep tone into it

One of the best ways to get an idea of how an exhaust sounds is to watch it on youtube.
Even tho the sound quality and the speakers in-ability to reproduce the natural deep tones may make it
sound a bit different then it would in real life, I find it'* worth the time to do some research there.
If you have a sub with your computer then everything sounds much much closer then it would in real life, the 3800'* seem to have a very deep tone that not many speakers like so they make it sound like crap.
But as the others said flowmasters on a v6 usually isint a good idea, and IMO flowmasters sound like
crap in general. Glasspacks with a resonator tend to sound nice, as do borla if you can afford that,

cam, heads, togs, 3" to dual 2.5", generic 4" single outlet exhaust tips:

went from no cat to dual polished dynomaxs - so so, not a good sound at all other than idle, horrid cabin resonance. Kinda hard to describe without a sound clip, but lets just say "untuned, uncontrolled sound" just blah.

no cat, no res, no mufflers, exhaust exiting under car after the rear 3" to 2.5" y - did for fun, could actually hear the car about 3 miles out of town when at WOT. "Sign of the apocalypse."

no cat, resonator, dual original 40 series flowmasters - had the nastiest sounding idle ever, especially with my old tune that had my idle speed turned down a notch. Sitting in the car at 55 mph for long periods of time would give you a headache. Seriously. Loudest mufflers ever on my car. Didn't even sound like a car during acceleration, just horrible. "Made baby Jesus cry."

Magnaflow 3" catalytic converter, no resonator (put one on, really didn't make much of a difference so we left it off) dual cherry bomb vortex'* - A co worker had on of these mufflers on his dodge ram, gave a nice stock sound but had a nice deep sound to it otherwise. Tried these, Borlas, and a set of magnaflows while the car was on the lift. All 3 are a non chambered straight through design, but the vortexs were very, very slightly quieter, cheaper and had a better sound. To our ears anyway, but we listened to that exhaust alot that night. Calmed the cam lope sound at idle which I didn't like too much but made the car nice to ride in again. Rasp during acceleration sounds much better.

But as previously stated, all 3800s sound like crap when they aren't idling. Keep the stock mufflers as long as you can.

btw, the catalytic converter silenced the rasp and interior resonance more than the resonator, and the combination of the two made no real difference. So the res was left off. Apparently in the GTP world thats blasphemy. But on my car that'* how it worked.