My response was to sort of go the other way and really force myself to consider NEED {not including shotguns since rifles were specified and not including a specialized small-varmint rifle since I made my list up thinking in terms of game animals}.

Having rethought the question, I would be quite satisfied with the same list, adding only a shotgun for shotgun-only required big game hunting areas and a .223 for small varmints.

So there is the Five I suppose.

Truthfully, though, for all big game hunting anywhere in the world, excluding dangerous game, I could get along quite nicely with just the 6.5x55.