Originally Posted by rwenzing
2003-back could have a problem with its 3 sensor system unless an X-pipe or some other solution was used to accommodate the single rear sensor.
Since you have a 2004+, you have 2 front O2 sensors and 2 rears, so a true dual setup retaining all 4 sensors and the cats should be fine. I don't think that it would give you any massive power gains compared to a single exhaust or split dual system unless the engine was highly modified.
Im pretty sure he would have the cut off the very last cat for true dual exhaust bob. The 2 banks with the 2 precats go into the big last cat, after the last largest cat it is 1 pipe. The last cat is like a "dual in-single out" if that gives you a better idea.