How about re-phrasing the question to specify two rifles that a hunter might actually acquire and hunt with ...

Some of the rarified calibers or chamberings mentioned here, like the 425WR what-cha-majig or the 550 Unobtainium, just aren't real-world practical. More for fantasy hunting or, better still, fireside daydreaming after a long day of ... fishing.

The goal of a two-rifle battery for big game should be 2 rifles that are readily obtainable and would be effective on 95%+ of BG species worldwide.

For me, those rifles are a 300 H&H magnum and a .404 Jeffery.

300H&H.

.404 Jeffery.

If limited to one do-it-all rifle worldwide, well, the choice is easier: my semi-custom .375 H&H BRNO 602.