I've not only taken bull elk with the 7x57, but a Canadian bull moose. No problems with them, or similar-sized African game like kudu and wildebeest.
Generally I've used well-constructed bullets in the 160-grain class for such game, including the 156 Norma Oryx, 160 Nosler Partition, the late lamented 160 North Fork, and 160 TSX. But would be perfectly happy to somewhat lighter bullets as well, especially monolithics.
