Well, i've hunted big bears quite a bit, and shot a few too. You didn't say what "exact" load would be used in the guns you listed, and that's the "most important" part!!

Personally, the others here have a LOT MORE respect for a 12 guage on bears, than i do!! And as i get to pick the load, i'd take the 300 Wby any day over a 12 guage!!!

Drilling Man