It seems every hard breaker I know has made five or six. I might of seen a seven once, can't remember clearly. I know I made a six once and it seemed four balls went in real quick, than some lucky caroms made the other two.
Never seen eight, though I believe it has been done.
Will never believe all nine went in until I see a video of it that obviously isn't fake.
I'd guess five or six is the most I've ever seen at eight ball so ten is a pretty good break lol.