I think the loudest two I experienced were Ted Nudget (with The Cars --- what a horrible match up) at the Pontiac Silver Dome in MI and Aerosmith with AC/DC (pre Brian Johnson before Bon Scott died) in Buffalo. I've seen Yes, Rush, Jethro Tull and Pink Floyd multiple times but they didn't approach those levels. Nazareth, after their hay day, toured smaller venues and hit a local club, but they came with a transport truck full of gear for a place that sat maybe 200 - 300. I had to literally yell at the top of my lungs into someone's ear in order to be heard over the band. That was just nuts. Goddo did something similar in my youth in an even smaller club.
When AC/DC backed up Aerosmith, Malcolm Young would get up on a roadie's shoulders and play a solo wirelessly while the roadie ran around the crowd. He doesn't do that any more.
I saw AC/DC again with Brian Johnson for the Hells Bells tour. They were not yet hugely popular, so they played at our local hockey arena which only sat about 5,000. I was 5 feet from the stage when they lowered the giant bell for the opening number. Good times!
I could start a whole thread on live concert experiences.