The more I think about, I can't remember (huh?) what the loudest concert I've seen has been. Many contenders over the years.
Iron Maiden, Metallica, Megadeth, Slayer, Overkill, Motorhead (who I mentioned earlier), Danzig, Soundgarden, Kreator, Destruction, Black Sabbath, Wrathchild (America), Queens Of The Stone Age, Sepultura, Ozzy, Corrosion Of Conformity, Whiplash, Anthrax, Voi Vod, Faith No More, Savatage, Forced Entry, D.R.I., High On Fire, Nuclear Assault, Exodus...many others I was either too high or drunk to remember...
I had my hearing checked about a year ago, my left ear is good shape, my right ear has some hearing loss in the upper registers...amazing considering how many of these shows I went to without ear plugs.