I'm not going to advocate anything in particular but have a few observations to share:

I work for a govt agency. I have several friends, numerous acquaintances, have researched this issue for my staff (we live and work in grizzly country=granted they are pretty rare this far south), have seen about 2 dozen wild grizzlies in Alaska and the lower 48. Been charged by a black bear (~400 lbs) and wrote a thesis on black bear behavior for my MS.

1) Our staff in Alaska use Brenneke slugs in a 12 gauge. The staff at Kenai Fjords killed 28 bears in defense of life or property in 2010.
2) We universally agree on pepper spray versus a handgun. I teach the use of bear spray, so I know its limitations.
3) At a recent workshop I palled around with a guy from Canadian Forest Service. He said, most victims they find have rifles still on their shoulders--They are THAT fast.
4) Whatever you use, it had better be in your hand. Rifle or handgun (or pepper spray in a holster), you better be holding it.

That being said, what do I use?:

1) First defense: Situational awareness and good woods sense.

2) Second chance (back-up): Pepper spray.

3) Third choice: Ruger 45 Colt with hot 300 gr hardcast lead handloads.

Is the 10mm enough gun? Yes, it could be. Or, it might not. That's the answer I would give regarding any handgun. The bigger and more powerful, the better.

A guy in Denali killed a grizzly with a 1911 in 45 acp last year. Took a whole clip but I've been where he did it and he had no choice==there isn't a tree for at least 5 miles.

Regardless, it's a **** shoot and you take your chances with whatever!