I find this thread particularly fascinating, and I hope more folks post on it.

I have read that if an elephant were as tough as a buffalo, nothing hand held could drop it. While such statements make interesting reading, they are of little value. Any close range charge by a large dangerous animal presents a difficult marksmanship problem, and thick cover increases the difficulty of the problem. The chance that you may not solve the problem in time interferes with your ability to work out the problem in the first place.

My experience has been with large bears, however a bear is not difficult to stop with a properly placed bullet, something not true of dangerous African game. I can however assure you that a large bear appearing suddenly at close range provides it's own brand of excitement. It also poses, to some degree, the same difficult marksmanship problem of speed, accuracy, and power. Of coarse to solve the problem, one must know where to put the bullet in the first place, and generally speaking, the bigger the animal, the less distinct the point of aim.