As far as personal experience is concerned, I used a wildcat .505 SRE and a .458 Winchester Magnum for my thick skinned dangerous game cartridges. My PH used a .470 Nitro Express DR, and I can truthfully say, I don't know effective his shots were. I knocked my first elephant down with my first shot, but it took a couple more shots from my .505 and a couple from his .470 to keep him down. When I complained about his shooting as unnecessary, he pointed out that we were only a couple of hundred yards from the boundary of a game refuge, and if the elephant had made it over the line, we might never recover it. I agreed that he had wisely contributed to the elephant's demise.
The other time involved a rhino charge. I was off to one side and the rhino was charging him. As he came abreast of me, I fired a shot which went into his neck, causing him to reverse course 180 degrees and head back the way he came. I put in three more shots, all in the shoulder area and my PH emptied his double rifle. A post mortem revealed that both of his shots had gone into the rhino's rear. One had keyholed and the other tumbled. Both bullets were recovered, having contributed nothing to the rhino's demise. The rhino made it about 150 yards before collapsing. He was already dead when we found him.
My first shot had been aimed in front of the shoulder as he rushed down hill, but acording to my PH, he must have seen me out of the corner of his eye, because he slammed on the brakes just as I shot. I was aiming at the point on his neck where the bullet struck, assuming that I needed to lead in order to hit the spot I intended to hit, the point of his shoulder. Two of my next three shots hit exactly on the tip of his shoulder and the third was a few inches farther to the rear.
My PH never fired another shot, either on that hunt or the next two I made with him. In fact, he was not even present when I shot my lion and leopard. I did have two gun bearers with me when I shot my leopard, both armed with double barreled shotguns loaded with buck shot, but they never fired them or had any reason to, thank goodness.
My PH passed on to his reward some years ago. De mortuis nil nisi bonum.