No. 45 Colt is more than enough to accomplish your mission.
The biggest decision you will have to make is how much gun do you want to tote around in a pure defensive scenario?
Back in the day I found myself in CA chasing a bear with my hunting buddy Lou, and the Robb boys from Utah. I had planned on using a Marlin Guide gun 45/70, and had a trusted 4 inch S&W Mt Revolver in 45 Colt on my hip. I had the S&W loaded with some sort of Nosler 260 gr HP at or around 1150 fps at the time. A fairly hot load for the S&W. We were using dogs and they hit a bear going up a mountain. They finally got this bear pinned down ahead of us. All total we were 3 hours into climbing this mountain. We arrived on the scene and the bear was cornered inside a small cave. Knocking the dogs out of the way, the only flashlight we had was a small mag light and the batteries mostly dead. Myself and one of the Robb boys down on hands and knees could only see the bears head about 4-5 feet in front of us, snapping his jaws at us and putting up a hell of a fuss. Crap! In this scenario the Marlin was just to big to maneuver around, so I snatched the S&W out. We could see nothing but this bears head, nothing else. Deciding that it looked big enough, and had 3 hours into this thing already, I was not going back empty handed. Hands and Knees in front of the small cavity and a half ass mag light, I decided to aim just below the chin and turned two rounds loose, real quick, jumped up on a rock next to the hole the bear was in. Now I am in a good position about 6 feet from the entrance, looking down. I forgot I had a Marlin Guide gun. Bear is snapping jaws, pissed off, growling and making a big fuss now. Even pokes his head out a couple of times, but the entrance is so small he just can't worm his way back out easy. Time is slowed, I decide to replace the two rounds I had fired, and was ready and waiting. Bear started working his way out, he was struggling to get his shoulders past the entrance, and when he cleared one side I started pouring it to him. After 4 more rounds he decided he didn't want any more of this and rolled down the mountain about 75-80 yards, and it was done.
I was rather pleased with myself, had a big smile on my face as I turned around, but damn, there was not a soul in site? The entire crowd had managed to move around the side of the mountain out of sight! HEH HEH..... WTF? They giggled as they made their way back when they figured the battle was over..............
I did not do a big bullet research on top of that mountain, but I don't think any of those HP's expanded, or done anything but pass through. Was not a big bear at all, about 200 lbs is all. But it was a damn good time and a bunch of fun.
I carried that 4 inch S&W gun around for a couple of years, taking a big 400 lb pig in TN with it, and two Mt. Lions in Utah. I never felt like I needed more.
I love 45 Colt, and have everything from Big Rugers, down to SA Army and Taurus, S&Ws, Anacondas, and even a custom built for me Dan Wesson with 3 barrels. I have loads that will do about anything you ever want with a handgun, tailored for the individual strengths of the various types of 45 Colt you might encounter. All 45 Colt are not created equal. You shoot different loads in a SA Army and the small Taurus guns than you do in the Anacondas and big Rugers. The S&Ws are somewhere in between.
A few years ago on our last trip to Alaska for bear I found myself trying to decide what to carry as a side arm. Obviously it was going to be one of the 45 Colts. But which one? Of course I started out with some heavy loads in the Anacondas and Ruger. Damn, too much, starting to hurt my hands! And the damn guns weighed a ton. I was not really having happy thoughts of carrying this extra weight around, and those heavy loads! After some deliberation, I decided to carry a 2 inch Taurus 5 shot lite weight gun, one that I had carried many a mile and never even realize it was on my hip. I had even carried this same little gun in Africa in two countries, and never felt under gunned. Shooting some sort of 250 Cast at 800 fps. I also had a 4 inch version of this same gun, and my Wife carried it in Alaska on this trip. I of course was hunting bear with 50 B&M, so the handgun was only if I found myself in dire straights. Figured if 5 of these 250 Cast in the face didn't get his attention, well, nothing else would either! LOL>..............
I have some fairly extensive data on heavy loads in various type 45 Colt handguns, so more than happy to assist you with that should the time come. Depending on the strength class of the handgun you choose. Bears come in all size classes, but a 250 Cast at 800-1000 fps can get to the vitals and get one off of you as good as anything. I would go for penetration, I would not worry about a HP or Trauma inflicting bullet with a handgun. Since it is defense, I would put much thought into weight and portability of the handgun. Of course, if you are young and strong, you can go to one of the big guns and run 300 gr CEB Solids at 1300-1400 fps and have a blast, but today I don't want to carry such weight around myself.
Today, if I found myself in exactly the same scenario, I would carry a Kimber Ultra or at most a 4" gun in 45 ACP, loaded with 200 gr CEB FN Solids at 800-1000 fps and carry a spare magazine.