I have never hunted Buff or Ele but would think the Double should be used first and foremost as a trump card,an elephant stopper when hunting DG with ELe encounters possible. That means the biggest Double caliber with solids I can handle for intial and followup shots--a 500 nitro. I can always have someone carry a 416 bolt and handoff the Big Double for other situations hunting Buff, etc.

I have no African experience but I think the Double should best be used for the purpose it was designed for-as a close range stopping/killing machine. Be it the proven 450-470 class of Ele stoppers with shooting parameters similar to the 458 WM or bigger Double classes above the 450's, that seems to be the natural niche the Double best occupies.