I have a feeling this won't be the release version on September 30, hence the "Candidate" word at the end. On the side note, the GM for iOS 9 would most likely be the same as the release version since it was released so close to September 16.
The 10.11 GM candidate installer was built on a later build, and there will be a release build that, if nothing else, unifies the developer and public betas.
When it comes to beta, I interpret stable as being relatively free from constant crashes and reboots. Just because you experienced a panic in a specific situation with several variables, that doesn't mean that other people using the OS differently will experience the same.
From what I have seen on the forum, (as a whole) El Capitan has been stable for most users who have taken the time to respond.
Yes sure. In this forum, even Yosemite beta 1 was super stable, and snappy, for most users. But truth is that is was perhaps the most buggy OSX release in the last 8 years.
What utter rubbish your POV is. El Capitan is probably the most stable OS since 10.6. Just because your shambles of a computer had problems is not our fault.