To the OP, if you plan on posting in the future, it will be helpful to us if you fill out your signature.
I had a 4" exhaust into a 5" elbow that ran through the bed, and Y'd into dual 5" mitre cut stacks. No muffler on a factory turbo truck.
The pros; they looked great and sounded great on the highway and let you hear the turbo more around town. I don't think the turbo noise was louder, it was just that it was closer to your head, allowing you to hear it.
The cons; Lost 6" of bed space, and couldn't put anything against them due to the heat. The were very raspy at anything under 2500 rpm's. As mentioned, they make a mess of your truck, constantly covering it in soot. (I would assume that this is not so much of a problem with "turnout" stacks).
I use my truck, and ended up getting rid of them for a straight 4" out the back. To me it sounds much better, and is worth it for the bed space I recovered.
You will definitely get more noise, but as long as you use large enough pipe (4" or larger), I don't think you'll have any cackle. But honestly, why would you want it?
Just my two cents. Good luck, hope it helps.