That muffler won't really do much for you.
I run two of the biggest Magnaflow straight through 2.5" mufflers I could find (true duals, one muffler on each side) with an X pipe and stock cats on my Vortec K1500 and I wouldn't want it any louder. The mufflers are from their RV line. But everyone likes something different, and I tend to go as quiet as I can while getting it to flow well and sound good. Your setup will be quite loud. Headers will make things a bit louder. Glad to see you are keeping a cat on there, that will help a bit.