Ive always been a bit weary of them. I should say that Ive never personally driven a car with them in, or seen any dyno results, but from the pictures Ive seen portray them as having less frontal surface area and less overall volume than some of the other vendors, and for the price, I am adamant that they are *NOT*worth it!
Id be intersted to see those test results performed with a set of Stillen ICs instead of the ARC ICs. And Id also like to see the test performed by someone else. That guy that posted to that board seeemed a bit....off... =)