I've now shot my 4 stack on a 26" 300prc, a 16" 6.5CM and an 18" 7PRC.
I don't have a dB meter, but I have tinnitus... And I assure you that even the measly 4 stack with 4"reflex is hearing safe in all those instances.
I can't imagine what a 6, 8, or 10 stack would sound like.