When I get a GT Im gonna get a pypes muffler delete but thats just me
... Honestly start looking around youtube and looking for different exhausts ... Heres a quick start and ask some questions 
http://www.newyorkmustangs.com/forums/exhaust-thread-t5249.html
http://www.newyorkmustangs.com/forums/exhaust-thread-t5249.html
That's the best sounding exhaust that I've found so far as well. Sounds so beastly, I'm just afraid it might be too loud.