Well, since your thread had NOTHING to do with NOS, I'll avoid that topic and stick with trying to answer your question and give you my opinion. The first thing I did to my car (pretty much the only thing so far) was a cat-back exhaust. It just seems like a better thing to start off with than a CAI if you want to add some bolt-ons. You probably won't see a huge improvement with either, but out of the two I'd say exhaust. Just my opinion...