I currently own 2 M29-2s (6.5" & a 4" version) and I find them brutal with full loads. Firing a fast (and accurate) repeat shot is impossible.
Even the 44 Magnum is marginal if you actually need to stop a big bear. If I really thought there was a chance of being being attacked by a bear I wouldn't go there. If I had to go there, I would want more than a pistol.
I'm thinking a 12 gauge auto (fast follow up shots) with an alloy receiver (for low weight) and an 18" barrel (compact) with a big, brightly colored front sight (for quick acquisition). A 3" Magnum slug in the chamber backed up by 00 buck filling the magazine. Put a sturdy sling on it and put it muzzle down over your shoulder. Practice bring it up and getting off a fast aimed first shot. Practice doing this a lot.
No, not as convenient as a revolver in a holster, but if you lose the lottery and get charged by a bear this is the gun you want.
SP-
There have been countless tests by the AK F&G and other sources that show buckshot being next to useless on large bears, so I would never recommend it.
I carried a Redhawk everywhere I went when I lived up in AK, and it wasn't very confidence inspiring when there were brownies around. Better than throwing rocks, but not much. Unless a person has stood close up and personal with those bears, they can't really grasp just how large they are.
Personally, I would much prefer a good lever gun like the Marlin 1895 or Winnie '86 with stout handloads or BB type ammo, than any shotgun, with any type load. In fact, when I came back to Michigan, the first thing I did was buy a Marlin 1895 just for protection against the big bears for when I went back up, which never ended up happening for reasons rather forgotten.
As far as the OP's ?.... take the 29/629 and never look back, but don't load it with the wrong ammo or you may as well have the 40. Buy some good hard cast BB or Grizzly ammo designed for use in a S&W platform, or load your own to the same performance levels and then practice as often as you can. In time the recoil won't seem as bad, and making fairly fast followup shots with accuracy is feasible. I'd prefer a good 280 grain or heavier bullet for penetration on large game over the original Keith design, but it will work.
BTW- there are tons of places to get the original Keith design from besides Dry Creek, but his are as good as anyone's, and he is a good man to deal with. I have a bunch of Cry Creek 44 Keith bullets here right now.
JMHO YMMV