I don't think there is much power to be had with the exhaust. I've been looking at it for my next mod not knowing what Rob's log headers may do for power. One problem on a V6 is the uneven exhaust pulses Placing an x-pipe as close to the engine is helpful there. I am going to use a Magnaflow TRU X-pipe muffler where the rear cats are. I'll have the front cats removed and pipes welded in their place with a set of PYPES cats meant for forced induction motors to go in when needed. Using mostly the stock pipes I will remove the resonator and use a Borla Pro XS out back as Borla's do not drone but they are as loud as the rest. I may even put a 4" round perforated muffler inline somewhere if I need to get it quieter than the 2 mufflers will do. I have noticed that the guys with cutouts gain very little, under 7-8 HP if they have a good exhaust system from the cats back already which shows the good system is giving some power as I think I read the cutouts were good for power in the mid teens. Should Rob's headers make 15whp+ I will add them to the system. Running 42% more boost than stock should make that much more spent gasses to be removed. Hopeful at this point anyways
PS: I got the magnaflow and like the design very much. As much an x-pipe as a straight thru muffler.