i've got a 3" inlet dual tip magnaflow muffler. my setup is... 3" dp, 3" test pipe, 3" piping, to 3" muffler. so 3" all the way through with no resonators, cat, etc.
i dont think its too loud at all, but i'm used to loud exhausts. its a deeper sound than my old greddy evo, but is a similar sound. looks sorta stock too, so thats a plus.
