Has anyone installed the Gibson 3" exhaust? It $615 it is comparatively inexpensive. Gibson is the only MFG I see make a HP claim: +15. I find this a bit dubious adn "salesy"... Torque numbers are far more important. how does sound level compare to a Borla S dual sys? Any experience out there? I want to upgrade the system but do not want to "ATK" loud.