I have not hunted bear, but have walked where they walk. I am fine with .357 Magnum. I don't own anything that shoots Supermag.
Phil Shoemaker, an Alaskan guide, does not feel that properly-loaded .357 mag is inadequate for grizzlies! He uses .44 mag himself, or at least did when he penned the recent article. His daughter wears a .357 K-frame sixgun. I am not going to put words in his mouth, and as I recall, he did have some instruction on how to use .357 against grizzlies. I take that as meaning I don't need to up-gun if walking among blackies.
Of course, I would not want to shoot a bear with ultra-expanding/fragmenting Federal Classic 125-grain .357. There is better for shooting big furry quadrupeds.