I remember reading a 5 gun battery for the world...the author chose...
.243 Win
.280 Rem.
.30-06
.375 H&H
.458 Lott
Each could be used to back up another on a given hunt, all are fairly readily available worldwide...
I think I might choose a 270/30-06 in place of the 280 and then a .300mag in place of the 06 for my 5 gun battery...