We just tested three Gen IV cars with Belanger headers, two had Mopar controllers and all three had different mufflers / exhausts on the same dyno, same day. In short, results were as follows:
1 - Corsa and Belanger exhausts were equally loud, 114 decibles outside the car.
2 - Stock muffler was 20% quieter than both.
3 - Corsa with Belanger headers made 10 more rwhp and 25 more rwtq than basic Belanger (Magnaflow) system and OE mufflers - 595 rwhp and 575 rwtq. It did have the Mopar Controller, so this could have helped hp & tq a bit, though one of the other cars didn't make the same numbers and it had the Mopar controller too but had OE mufflers.
4 - OE mufflers sounded a bit better to most outside the car at WOT, crisper. Quieter seems to cost about 10 rwhp or a bit more.
5 - At cruise, inside the car, OE muffler is very quiet - no drone even with headers, Corsa is next, basic Belanger system is much louder and drones (this is just our opinion).
As exhaust noise is highly subjective, your opinions may vary.
Dan