I scanned through this long thread to see if someone else had already pointed this out, but I didn't see it.
In the class of big game cartridges for BIG game, there are several in the 5000 - 6000 ft-lb class: 416 Rigby, 378 WBY, 458 Lott, 470 nitro-express (NE), 500 NE, etc.
Then there are a couple in the 7000 - 8500 ft-lb class: 460 WBY, 600 nitro-express, 577 tyrannosaur, plus a variety of specialty/wildcat cartridges.
And then there is the 50 bmg... with 14,000 ft-lb of energy... It is basically double the energy of the most powerful elephant/rhino cartridges around. This is not a small step up in energy... going from a 243 to a 375 H&H is doubling the energy, so imagine that there is as much difference between a 375 H&H and a 243 as there is between a 50 bmg and the most powerful elephant cartridges around.