Yeah, considering how poorly most of us do when in a hurry, bring able to quasi reliably put a half dozen rounds down range seems like it ought to up your odds a little as opposed to hoping for that one good one.
Although if it was a black bear I'd have to think real hard about escalating versus just standing tall and hollering back. Most black bear charges are bluffs so your best bet is usually to just stand them off. They usually aren't that interested in tangling, even momma's with cubs will usually give you a fair chance to retreat.
If it's a grizzly I wouldn't give you the same odds as a pickle in a sandwich with most handguns though. 12 gauge with slugs. Otherwise your best bet is to just poop your pants, play dead and hope he don't like the smell.
I'm gonna have to disagree with you on a couple of points, Ryan. The conventional wisdom up here is that browns are more likely to bluff charge than black bears. While blacks are usually a bit more shy around people (unless habituated) they are considered by many to be less predictable on the charge. And while playing dead is recommended for brown attacks (at least at first) they don't have a great track record with black bears. Browns will often paw at you until they're satisfied you're not a threat. If a black bear sets upon you, I think you're more like to suffer traumatic weight loss.
As for caliber choice and follow up shots...
The time you have to react and got a shot (or shots) off depends on your state of readiness at the time, the distance between you and the bear, and the bear's motivation level. A bear can cover a lot of ground in real hurry when s/he wants to: about 10 yards in 1.5 seconds from a standstill or about 30 yards in the same time on a dead run, based on cases I've read. How many rounds can you accurately put on target in that time? From the holster? Me, I'd rather get 1 or 2 heavy hitters on the threat rather than 3 or 4 rounds that are far less energetic.
I'm a 1911 (Kimber!) guy and I love the .45 ACP round but it's really low on my list of bear guns. I'd consider .45 Colt (handloaded or specialty) in a Ruger of some flavor but I prefer .44 Magnum. Like others, I prefer a 12ga shotgun even more but in my usual fishing situations, it's not as easy to carry or deploy. That said, the best gun to use is the one you have with you. Many years ago, a fellow who worked at my local fly shop took down a brown with a .357 Mag in a DLP shooting while on a river fishing trip. Another time, a friend of mine was relieving himself in some bushes when a black bear charged him. Almost literally caught with his pants down, a bear attack was the last thing he expected in the locale but he successfully responded with his CCW piece, a .40 S&W semiauto. He zipped up afterwards.
But those are just my opinions. Even though they come around the house from time to time, I've never had to shoot a bear or even come close to doing so. Fingers crossed.