catless does not really mean louder in all aspects. i am catless now and am no louder until 4500rpms+ and even then its not that much louder.. the size of the pipe has more to do with sound. cause either way that turbo is gonna block a lot of sound.. compare your catless wrx to a catless NA car.. much louder cause they are not turbo'd...
and the idea of having a highflow cat for somepeople is.. cop pulls me over, see's a cat i have a better chance. doesnt see a cat im screwed..
and some people are actually environmentally conscience...
and you really will NOT notice a difference with a highflow cat, until you are trying to push every 100th of a second off your 1/4mile. to trying to reach a high high hp and you are a couple hp away and are trying to squeeze in every bit of hp.
cause there is only like a 3hp difference with a highflow. so catless is not so necessary unless you dont wanna pay the extra 200 bucks.
keep it in the dirt.