Hey John, you might want to pm Steve (32Krazy!). He has Removed the secondary cats, resonator, and installed a magnaflow X pipe. From when I talked to him, I believe that he said that the main difference was that the X pipe smoothed the tone out quite a bit, as the exhaust flowed better. As far as performance goes, I still think that it is going to take installing headers to reap much benefit from the other exhaust mods.