Unless your cats are plugged, it has been my experience that when an exhaust is uncorked it revs more freely but that doesn't necessarily mean your torque is improved on the bottom end. If you were pulling a trailer weighing 1200# and clocked the time and distance to go from a standing start to 2500rpm with both setups, I'm relatively certain it will be slower and take a longer distance to hit 2500r's with the opened up exhaust.(imo) Without the trailer you would have a harder time documenting the loss, but it would still be there.