My motor is rated at 375 HP and dyno'd 306 at the wheels, which is cool for me. But.....more power is ALWAYS a welocome friend. And louder would be cool too....I think
FYI I had a 5.0 mustang years back and removed the mufflers and the car definitely felt slower. Had the same issue on a newer Tang GT when mufflers were removed. Not sure if I lost HP or torque, maybe both. I rememeber reading you usually lose one or the other when tweaking your exhaust system.