When I saw Yamatsuka Eye with Merzbow that was loud. Loud enough to pop a few ceiling tiles from a Toronto club they were at. The old ears were ringing for a few days...
Which reminds me, Mother Acid Temple are playing a tiny local club soon, that could be loud.
Only gigs that caused me prolonged ear issues were Dinosaur Jr and Little Steven of all people; played a local hall around '86/7 (so height of his fame really) but there were only a few dozen people. Sound was way too loud and just echoed horribly, half the audience promptly disappeared to the bar. Give him his due though, carried on like a trooper, quite a show really.