Looking into picking up this kit but I've noticed there's two options: CAT or no CAT. Just want to see who has what and how it's running. Not a big thing to run without a cat in my area as we don't test.

 

No cat, but it depends on where you live.
New car, wont need testing for a few years. And you can swap for it.

 

CAT will effect response time. It did when i built a 240sx, but its a tC. Just my input. Also depends how much boost you're planning to run. If its < 12 psi or so... you wont notice a drastic change in response or high end.