Hardest hitting, yes.
Jack O'Connor recommended them for tigers.
It wasn't mentioned.
There is a lot of stuff on spray in Nonfirearm Weapons. Anatomical differences make spray much more effective on bears than on humans. Remember, they can smell food for up to three miles.
I would rather dissuade a bear than rely upon stopping it.
I carry pepper gel and a pistol--bot not for bears.
One will not walk down the trail with a pistol in hand. it has been years since I saw the video, but as I recall, the shotgun was ready to shoot.
For perspective, an average man can charge at around 5 meters per second. A bear can charge at perhaps 15 or 20 meters per second.