As a guy who does tramp around in the bear woods pretty frequently and hasn't been eaten yet, I'll give my 2 cents. I'd suggest you carry whatever you can make repeated fast hits with. I don't know of many handgun rounds that will do the job with just one shot. I carry a Kimber ultra carry 45 when I backpack in the black bear country. I carry a heavy loaded 45LC in Grizzly country. Both are more psychological comfort than anything else. I had to hike 3 miles back to camp in the middle of the night once( in a nasty thunderstorm) in grizzly country after a horse tried to kill me. I had my 45LC and a flashlight. I am under no illusions when it comes to handguns for bear defense. In the highly unlikely even that I ever have to use my 45's to defend myself, I will most likely be shooting the bear OFF me. Pistols just don't kill fast enough. Their main advantage is that you ALWAYS have them with you and they are better than fighting bare handed. We keep 12 gauges in camp and close at hand when camping in grizzly country. We've had them camp and it's not fun. Too many people, I think, have an incorrect scenario in their heads of how a bear encounter would go down. They are ambush predators. They nearly always see you before you see them. It will happen VERY fast and at very close range. You won't have time for much precision shooting. The one guy I know that killed a griz in self defense did it at 3 FEET with a 300 win. Bear landed at his feet. He fired his remaining rounds down through the top of its head. The biggest problem with backpacking is weight. No one wants to haul around an extra 4lbs of hand cannon, so the pistol gets left at home. Whatever you decide on, practice a LOT. Get it out fast and make fast repeated hits on a dinner plate sized target at about 3-4 feet. For handgun hunting, any of the calibers you mention will get it done. I've been intrigued by the 10mm for a long time, but it's an itch I haven't scratched yet... My 45's keep working, so that's good enough for me. Please understand, I am no expert when it comes to bears. I hope I haven't come across as someone trying to act like an expert. I'm just sharing my experiences and opinions, nothing more. Take them for what they are, just freely given and shared words.