by removing the two rear cats you will still pass emissions, yes it will alter the sound alot, and in my opinion is stupid on this car. Some cars yes and some no, my srt-4 yes huge amount of difference in performance and sound but that is turbo, on this car you will not notice a difference and the sound will be horribly cheap sounding. i thought about it but installed my exhaust and wouldn't want it any louder or any different sounding i know how raspy it would be without cats, if removing all cats the light will come on and you would need to do something with the o2's. I am planning to add high flow cats in the two rear ones if anything with my exhaust, but not even sure if i will bother with them. Id say the stock cats will flow fine for what the crossfires got. Its not always based on getting the least amount of restriction possible, some cases you can lose power, depends on the car.