I had a set of flows 40's that I transfered between 3 different trucks
They do have a great sound but I just bought 50 series to cut down on the interior resonance. I'm also putting a crossover in the new system. With a 476, headers, and dual 3" pipes it should be plenty muscley trough the 50's while allowing the lady and I to hold a civilized conversation while cruising.
That's for a cruiser. If it were a rod I'd go with something rowdier.