I'm running a Flowmaster 40, now. I honestly can't really hear much of a drone on the highway over my tires, but it doesn't have that normal V6 high-pitched scream. It's a lot deeper, and sounds more like a short block V8.
And as for the inlet/outlet, unless you've completely replaced your whole exhaust, then the pipes run 2.25". You can get a nicer sound by running a larger outlet tail pipe, but I wouldn't put on anything bigger than a 3.5".