I read just this very thing years ago in field and stream only the distance was 25 yards. The research was done by Ballistic experts and Grizzly Bear hunting guides. They listed the top thirty and I don't recall all of them but the number one stopper was the 458 Win Mag. At close range velocity is not the best thing to have on your side. At close range it puts to much stress on the bullet. The 30-06 was in the top ten as was the 45-70 and 12 Ga shotgun. They said you have to be able to hit a target the size of a grapefruit to stop old Grizz short. Recovery time from recoil and the ability of the bullet to hang together were critical. The old 303 British was up there a ways as well. The claim only a brain shot is a sure thing once the charge begins. Somewhere I still have that artical.