A friend of mine put a high flow cat on his 91 Civic si, got the performance boost he wanted and quieted down his exhaust note.

I don't know how honda engines work with gutted cats as I am new to them, but many modern american motors get less performance when you gut the cats. They need a certain amount of backpressure to build RPMs more effectively. Cars smell a whole lot better when they have cats and won't tip off your competition if you own a sleeper car.