I have Race Pro's on my Camaro and they are about as quiet as I want for normal driving. Step on the pedal hard and they are going to let everyone in a wider area know that the car is around...
On my '38, it came to me with unknown mufflers and the wife complained it was too loud. We have used the car to pull the camper and it was rather annoying after a few hours and down right aggravating after 10 hours. After reading way too many reviews about mufflers, I changed them out for Dynomax Super Turbo's that MOST of the reviews said were too quiet on their muscle cars, not enough growl.. LOL They were quieter than I expected and I'm happy with them, but the noise analyst still wasn't entirely happy, but doesn't say much anymore.