I can recall some insanely loud gigs. I remember a Crowbar gig at the Underworld many years ago. Man my ears were wrecked beyond belief. Now the Underworld here in London is a smallish 500 max club but it felt like they were using the backline for Wembley Stadium in there! Another one that comes to mind is Megadeth back in 95. Marty's solos especially were piercing through to my timpanic membrane like you wouldn't believe. The quietest gig that I recall was Maiden at the Brixton Academy a few years ago. It was so quiet that you could hear people's stupid chatter louder than the music if you were standing enough away from the stage. It's amazing how some small things like this stay in the brain a long time.