Headers?... Cat back?

I have a 98 xj that I am ready to work on the exaust. I have the k&n intake so now it's time to get the air out!! I want to know if it's worth the money to do the whole thing, headers back or if a cat back system would be sufficient. Obviously looking for performance and mpg.

If you can afford it, an aftermarket header and an opened up exhaust will help. Definitely get a custom downpipe/add a piece of flex pipe before the cat. I would 2.5" all the way back. I recommend Magnaflow/bullet performance mufflers or aero turbines. Custom exhaust will be cheaper than the name brand cat-back kits.