Samurai and and 96GSRteg have good points. I grew up reading a crap load of Sport Compact Car... which didn't last, I think, mainly because it actually incorporated too much science, fact, and logic than the demographic was typically interested in hearing... I think they were more interested in making their cars simply look or sound quicker/faster, without actually being either.
They dynoed and tested and dragged cars many times and across the board supported the idea that removing a cat was simply idiotic with regards to getting worthwhile gains out of a motor. The gain of a couple ponies at 7500 RPMs was never worth the loses in the other parts of the power ban, not to mention the mass s***ting you're doing all over our breathing air year-round.
If you're going to upgrade for the sake of increasing your car's performance, do it right... or wait until you can afford to do so. I'm probably about as broke or more so than anyone here and, yes, I LOVE driving a quick car, but I'm not going to make the rest of the world pay for my poorly-researched performance experiments.
Start with creating back pressure on the front end... in other words, get more air in... intake/filter, manifold, turbo/super, higher-flow injectors to match the increase in air, more efficient ignition, etc. Then have someone with some know-how determine what kind of exhaust you will need to maximize gains... header, high-flow cat, cat-back of a reasonable and usable diameter, etc.
