I will take DM's word over most here because he has been there and done it. I have hunted the big bears as well and have done so with the 30-06, 45-70 and 35 Whelen as well as the 44 Magnum. Velocity is not always the answer here as lighter bullets at high velocities can often blow up on big bones. I would pick the 30-06 with a 200 grain and up bullet over any of the 300 Magnums using lighter bullets. However the 30-06 or any of the other bigger 30 calibers including the 30-40 Krag with 200 GR or heavier bullets perform well on the big bears. You don't need a cannon but you need a well constructed heavy bullet that will Penetrate and break bones. In its day the 30-40 Krag with 180-220 grain bullets was a top choice for big bears, Bears are no tougher now that they were then Nor are the bear hunters.

I believe that amoung other calibers, DM used the 338-06, 30-06 and 7MM ReM Mag as well as the 8x57.