Here's a bear vs. .45acp article:

http://www.thefiringline.com/forums/showthread.php?t=298031

This guy saw the bear (400lb black bear) from a good distance away, and emptied his gun into it. I think at shorter range, he'd have been a bear chew toy.

With regard to stopping an attacking bear, vs. hunting, it's important to keep in mind the two incapacitation mechanics: damage to the CNS and blood loss. A brain or spine shot on a charging bear is something you're probably only going to do if you get very lucky. Blood loss is problematic, because if you don't poke a big enough hole, the bear's fat and fur will tend to plug the external holes up and slow the blood loss. Plus, it just takes a bit of time for a bear to bleed out. That's why shotgun slugs and large bore rifles are popular.

My personal plan in bear areas is bear spray and a 1911 for backup. I might consider a lighter weight magnum revolver, but that's just not in the budget anytime soon.