You're going to hear all kinds of stories from people that have never shot a big bear with anything, they seem to be experts on all things that they have no direct knowledge about. I'm not one of those, I'm just a guy that has an opinion about what I prefer to use to protect myself with in the woods.
Personally I feel that you should shoot the biggest caliber that you are comfortable with. By comfortable I mean that if you can get 3 shots in to a realistic kill zone in under 3 seconds then that's the gun that you should be using. All this talk about what caliber is best means nothing if you can't get rounds in to the kill zone when a big animal is running at 30 miles per hour straight toward you. A few years ago there was an older man in Alaska, a professional hunting and fishing guide, who killed an Alaskan Kodiak bear that charged him. He killed that bear at just a few feet from him with a small framed 9mm. The bear died and the man wasn't even injured so caliber isn't all that important (within reason) as long as you have the right ammo and you can put the bullets where they need to go.
I live in rural Montana in the middle of Grizzly country and I have both revolvers and semi-auto pistols, which one I carry just depends on how I feel that day, if I'm tired I'll carry the XDM 10mm, if I feel good then I'll carry the S&W 329 PD lightweight .44mag. I've practiced with both pistols but not nearly enough to really feel good about my skill level, but I'll still carry one or the other if I don't want to carry a rifle, if I'm really scared of running in to a life threatening situation I'll carry one of my short barreled .308 rifles. I carry my pistols in a chest holster so I can keep them from getting packed with fouling that might prevent them from functioning properly. And being that they are easy to remove from the holster, I can check them from time to time to make sure that they are in good condition.
In a real bear attack you wont have the time to get more than a few shots off, maybe 3, so capacity isn't nearly as important as most seem to think. A revolver isn't drastically more dependable than a semi in rural country (the proof is that no military issues a revolver any more - semi-auto pistols are actually more reliable than a revolver when they are covered in mud, twigs, grass, etc.). In my opinion the most reliable pistol in the real world is a striker fired gun (I'd of said weapon but then I'd have to listen to some crazy talk about the definition of the word). A striker fired gun has no openings that will allow crud to get in to the mechanism and prevent it from operating. Revolvers earned a reputation for being more reliable back in the day when 1911's, Browning's, and Luger's, were popular. Back then the technology of semi-auto pistols was in it's infancy and they just weren't as reliable as they are today. Part of that is because today we have better powder, primers, and bullets, but it's also because the designs of some of the semi-autos just weren't very good.
If I were in your shoes I'd buy the XDM 10mm and practice a lot.
