From what I've read doing the exhaust is a waste of money, the stock system is very efficent, especially on the 5 gens up. The only real gains you will get is with a header and only maybe 8 hp. On an older CRX or 4th gen you'll see much more gains with a header because the stock one is a POS 4-1 with only one pipe going into the cat, the newers ones have two the same size. I really felt it in mine, but the newer ones just don't see the same gains. Unless you have a B-series which needs a better exhaust because it makes more exhaust top end with the high lift cam. I'd guess you'd only get 5 hp with a new catback and its louder and more likely to get you pulled over and you sound like a ricer. A catback costs like 500 bucks and gets you 5 hp, and it has downsides. I think a header is all you really need. Put the $500 towards a swap or something.