I can't make up my mind. On a FIPK or a Hooker Cat-Back system.
Which will give me the most gains?

 

Well, you already have an aftermarket cat-back, so go with the FIPK!

 

I bought the car used about 4 months ago.The cat-back system that was installed by the previous owner is about 5 years old, and there's small hole on one of the muffler outlets.
The idea of replacing just the muffler has crossed my mind too.

 

I would definiltly go with a K&N FIPK, that will most definitly give you more power then a catback. The hole near the outlet shouldnt really matter, but if you were gonna replace the muffler with an SLP one they are like 200 bucks. Get a Flowmaster muffler for about 75 or a Hooker one for about the same price and still get your cold air because those together would cost the same as a catback by itself.

 

What kind of SLP system is on your car...is it the "2 on the left"?