Well, it is a bit more than anecdotal. Most of the glass breaking stories started with my Scientific American article back in the 70's. I had a large O. scyllarus that took out the glass of an "Instant Ocean" aquarium flooding my office. Given that the glass was double glazing, I was impressed. I have also lost a few photographic tanks constructed of ordinary window glass and have lost a few regular glass tanks when animals started digging in the corner, hit something hard, and as they do in the field, chipped away until the glass chipped and the tank leaked.
For dramatic effect, when BBC shot "Fasterst Claw", I trained a large male O. s. to break through thin glass and the slow-motion film of class flying in all directions has perpetuated the story.
Bottom line, a large O.s, say at least 6 inches or a very large Hemisquilla can break standard 10 gal. glass tank. It is unlikely that they could - or would - break a larger tank using thicker glass, although they can chip edges and cause leaks. Any small smashers under say 3 inches couldn't break anything thicker than a microscope slide.
A Postdoctoral Fellow in my lab is curretly measuring the striking force of O.s. While the data are preliminary, the results are fairly spectacular and hopefully we will be publishing them soon.
Roy