well i do agree that the high flow ones arent exactly a miracle worker. there is some restiction in a cat. notice how much louder an engine gets when you cut one off. thats because they do mute the sound down to a certain degree. they almost act as a tiny muffler, yes the benefits of having one out weigh not having one because your engine does run better with one, on the newer stuff anyway,
now the design in the highflow cats isnt exactly like the old ones. they are made of different material. so they do do something, there just not worth spending all that money on. the dollar to performance ratio is def. not worth it. so IN MY OPINION, just leave the cats alone. upgrade the size of the pipe, and run the muffler of choice.
now please, i dont want to start a flame war, this is just my own opinion, i am in no way pushing my thoughts, or saying there exactly perfect. so please dont respond saying im wrong unless you have significant info as to wy im wrong. thank you in advance.