I've got the whole Calimini system. Header and cat back pipes and muffler.
Sounds really good and I think it gave the engine a boost. Seems to spool up better. It's hard to tell because I did a ton of stuff at the same time. Exhause, gears, tires, lockers, winch, and body lift.
I havent seen the need to remove the cat yet. Everything seem to flow fine so why not run one?