That's a complicated question that ultimately boils down to "it depends." Barrel Length, Ammo type/velocity, and suppressor type/capacity all play a role.
I would assume a 16" rifle with a good can will be hearing safe or very close at the ear. I think MAC has a video or two of a suppressed 6.8 SPC rifle on youtube where he meters it. I think Lonestar Boars also has a few videos regarding suppressed 6.8.