I have a C3 Pro as well. Wish the dang thing didn't whistle whenever I turn my head 15 degrees left or right. My dad lost some hearing working in field artillery and I don't wish to have that same problem. I use the OSHA ear fatigue limit charts as a guideline. I also think if the exhaust is ~3dB quieter than the wind noise at my ears on the conditions I ride steadily, it's quiet enough that it's not going to be the driving factor in hearing damage, so I should spend my efforts focusing on something else.
Any time I hear my ears ringing after a ride I know I screwed up and I spend some time evaluating how to not make it happen again. That's why I got the C3 pro in the first place, and I now wear earplugs for any ride over ~30 minutes.
The Arrow with dB killers installed is ~3dB quieter than stock, and with that setup and freeway driving conditions, wind noise drives hearing fatigue and exhaust is a secondary source. Keeping a catalytic converter has the effect of reducing the noise level as well (most aftermarket exhausts do not include one). Mobcrimeboss bought the termi slip on and did a great thread on how he went through and basically gutted and redid the entire exhaust to his specs, and the end result was a quieter exhaust and a sound signature he said he preferred - it's worth a read and may be worth PMing him.
Since they are quieter (and more restrictive) OEM systems than elsewhere, I expect you could find someone in Japan to trade you stock exhausts if you pay shipping - many there seem to prefer the non-Japanese exhausts. Finding an English speaker would be the bigger challenge there, but a few users on this board live out there.
Bottom line, if that's the holdup but you like the bike enough that you are willing to invest some effort and maybe money to address it, you will be able to make the exhaust on the bike mild enough that exhaust related hearing fatigue will not be any greater a danger to your hearing than riding any typical motorcycle.