I have 2 cars, both with 505”. Close in power. One dynoed at hair over 600 hp and maybe the other 650-660 hp based on track/ weight /et-mph comparisons with eachother. Both just about 10.4 and 10.6:1.

1 has 2” hookers into 3” ex and x pipe using Dynomax Ultraflo 3” mufflers. Sounds good.
The other 1-7/8” hooker headers into 2-1/2” ex with x pipe and into Magnaflow stainless welded mufflers. Both dumped at axles. The Magnaflow system, even though smaller and slightly less power, sounds better to me. Just has a nicer sound to me. Both perform very well in car.

At track, the Magnaflow system lost .15 et and 1 mph in back to back testing same day within an hour of eachother.