I know guys take a DG rifle and a lighter, non-buff rifle combo and get away with it. I think it is more prudent to take two rifles that are legal and appropriate for the largest game you plan to hunt, just in case your big rifle goes tits up. That would make a 9.3x62 or 375H&H the lightest prudent second rifle, imo, since both are legal for buff (and elephant too.)

JPK