I doubt that bears read gov't reports or ballistic data for rifle cartridges. I live and hunt in N. Idaho grizzly country. There ain't a lot of them but they are there. We can't hunt grizzly up here as they are protected - and rightfully so.
I hunt deer, elk, black bear and hopefully, someday, moose (just got my rejection slip for a moose tag again..)
Like everybody else here when I hunt I have the rifle I hunt with (duh..) which in my case is a 30-40 AI. I have never seen a grizzly here and if I do I hope it is a long ways off.
If I was hunting grizzly I would use my rifle - which is ballistically the same as a 30-06 - and would not feel undergunned. If I were worried about bear defense alone I would carry the biggest, baddest gun I could lay my hands on.
I would be lying if I say I never think about the possibility of encountering a grizzly bear while in the woods, but I'm much more worried about meeting up with another ****** off cow moose. Once was enough on that score.
But, back to the topic - good grizzly cartridges. Anything that qualifies as a big game round will kill a bear with good shot placement. My hunting partner killed his 500lb. grizzly (while he was living in Canada) with one shot from a 6mm Rem because that was the gun he had with him. He's one hell of a game shot, by the way. Everyone I know who has killed a grizzly used their regular hunting rifle.
I don't know why I always respond to these bear threads...possibly for the same reason I watch Mob Wives...