I have run the factory setup on my 88 with the exhaust cut off behind the cat and a turn-down welded in. It was surprisingly decent. Not too loud, but sounded like she was breathing a little deeper.
Current setup is tri-Y full length headers with 2.5" true dual and Flowmaster Super 40s, no cats. Deep, loudish, no drone. Exhaust exits diagonally out the back corners. I dig it, but as with all these setups, it's a preference thing and you may not get it on your first try unless you find a setup you love on someone elses truck and just copy it.
BTW, while I'm sure 3" headers and dual exhaust will win the HP battle, traditional exhaust theory says that you will compromise bottom end torque for top end HP. For me, that's a losing deal. But if you're mud racing or whatever, maybe worth it.