Don Dick,
Have you ever seen a heart shot deer fall to the ground, get back up and run up the tree next to you, then run down and go several hundred yards through some of the nastiest terrain you will ever see.
If the primary use for this weapon is for bear, the bigger diameter calibers are better, 444, 45-70, 450 marlin. Like I stated before a smaller hole plugs up easier, especially if you are doing a fall hunt when the bears are trying to put on a lot of fat. Will the other calibers work, of course they will, like Don Dick said, it is shot placement. Also a little known fact, more people are killed by black bears than by grizzly's