I saw Motorhead open for Ozzy ( Blizzard of Oz tour, also with Joe Perry Project), indoors and I don't remember them being that loud in Springfield, MA civic center.
I remember seeing Pantera in a large club, after the Agora Ballroom closed or moved, in West Hartford, CT, on the Far Beyond Driven tour...definitely louder than the size of the club could handle. Bass and kick drums were like getting hit in the chest.
I saw Slayer at the original Agora in West Hartford, CT back in the mid-80s, probably Reign in Blood tour, and I remember that being very loud. I don't remember much else tho'
I saw VH open for Sabbath in '78 on the Never Say Die tour, and on VH2 tour...neither was louder than usual IIRC.
edit: Almost forgot, Robin Trower at the Palace in Waterbury, CT, late '70s or early 80s, it was very loud