You should get alot of opinions with that question. Heehee!!
See my albumn for some of my pics. I like the KD especially for the cat.
I suspect whatever you get will sound different after it gets seasoned, it gets softer, looses a tiny tone. That should be true for most I would think. Maybe we all just loose some hearing over time??? LOL
Aside from the opinion most should agree you need a see-thru system; see thru muffler, see thru cat, see thru pipes.
I suspect for the hp range, 3.5" would be plenty. Anything bigger than 3.0" for a downpipe would only be a bigger pain in the butt to tease thru the tight spots. But if you like bigger tailepipe outlet for looks... hey, it's your ride, pimp it as you like. LOL
One think I don't like is a gm-x turbo with a straight thru exhaust. It sound like a sand blaster probably due to the restriction (shhhhhhhhh sound).
I have similar exhaust on the Suburban project, but we don't have any miles on it to really speak of, so it may still be a little new.