I have 2016 3.8 R-Spec. The Stillen Cat-Back added 12 hp and sound very deep base clean, not offensive put attractive. Secondary cats swipe with Ark racing Test pipes increases hp slightly more (maybe 5 hp) and made for the best sounding combo I have ever heard. This video is not my car but exact same setup. ->
3.8 with Stillen and Ark Test Pipes (Listen with good speakers or a headset to hear how deep the bass tone goes, its unrivaled).
This Thursday (September 2nd, 2021) I'm having a 75 shot of nitrous installed. Can't wait!