The .45/70 will kill a undisturbed Cape Buff' BUT if it is wounded by a bad shot and decides to stomp you into the ground the .45/70 may not save you !I think a .416Rigby would be better or better still a .470 Double ! Talk to your PH and if he backs you up with a bigger rifle it may be OK then again some hunters use Handgun or a Bow !so the .45/70 looks pretty good compared to them. In the end it is your hunt and if you know the risks and are happy use the .45/70 .

Steve