Very. Although, the .450+ bores do have an advantage in this department due to the larger bullet diameter (which punches larger wound cavities through vital organs and causes the game to hemorrhage from blood loss quicker).
This is particularly important, because you'll have to use non-expanding bullets for elephant hunting. So you'll have to rely on sheer bullet diameter for creating these wound cavities, rather than any form of bullet expansion.
Still .416 caliber is more than adequate. Except in very low visibility shooting situations such as terrain with dense foliage.