It’s great you use earplugs, everyone should! I like my bikes loud but at the tracks that neighbor the towns library, where our bikes need to be whisper quiet, I think 6dB might be enough. Better than putting stock exhaust system back on
I don’t think 6dB less is enough to not need earplugs, earplugs are great for wind noise in the helmet.
On bikes that rev higher/ have a different tone, the exhaust note resonates in my helmet but on these deep ducs I don’t get as much of that