I see no reason not to use the 300 Wby on any sized black bear...just use a good 180-220 gr. bullet and place it well. Why give them a chance at all??? :roll:
As for big grizz, well, I'd be a little shy to pack a 300 Wby out after one, with so many better options out there. If I had to, I'd load something like a 200 gr. Barnes X. A 8mm, 338, or 375 would be a much smarter choice!