Man, for a 4 year old thread this thing really has some legs!
So, I'll add a bit and ask a question. It seems to me that most of the posters, in a defined set of circumstances, are all correct, at least to some degree. Sometimes you need expansion and sometimes you need more penetration. So, my question is: "Who ever said you had to load the same type of round in all six cylinders? Why can't you load the first round an XTP or some other good expansion round and the second round a Hard Cast for penetration then alternate them."
Yes, I know, when a bear is charging time is very short and you may not be able to get off many shots. But, in some or most circumstances, I'd guess you can get off at least 2 shots. So, that would be one good expander and one good penetrator.
I personally have been in a bear altercation and put it down with a .357 loaded with BB Hard Cast. Yes, it worked and yes it saved my hind parts. But, the experience taught me this: "I want the biggest thing on my hip that I can shoot competently when I'm in the woods." So, now my constant woods companion is a Model 69 which, after a good bit of range time, I can shoot nearly as well as my Model 66.
Be safe y'all.
Bob