I'm just a gun geezer, Rifleman, not an audiologist. One thing I've found over the years is that some folks just have "tougher ears" than others. I've met lifelong hunters who never had ear protection when they fired their high powered rifles, and still have excellent hearing, and I've met people who had measurable hearing loss from a single gunshot in close quarters.
As a rule of thumb, lower pressures mean lower sound levels, but there are many other factors.
I look at it this way: active hearing protection is a valuable and relatively low-cost accessory that most shooters use regularly for their hobby once they've tried it. It doesn't cost anything to keep it next to the home defense gun in the bedroom. If there's time to put it on, fine. If there isn't, well, you'll have to go without.
For much of my life, the gun next to my bed has been a .357 Magnum or a .357 SIG. It will be tonight, in fact. If the door is kicked down too fast for me to get to the active muffs beside the bed, that gun is there to keep me from being killed. I want ammunition that will stop the threat as soon as possible. If it's not stopped soon enough, the price goes far beyond a bit of hearing loss.
The bottom line is, how much will we hear in the grave?