Hello there! Alright, I think you laid it out pretty well. I am mostly interested in Buffalo, Hippo and maybe far in the future a Lion so no Pachyderms (unless an amazing deal comes up on a Rogue or wounded animal) or Rhinos are on my list of future hunts. That being the case it seems like either the 450/400 or the 450 N.E. would be about as much rifle as I am going to need I think...!
As mentioned before, the .470 is a ballistic equivalent of the .450 including recoil. And as @AZDAVE stated ammo is more available for it. Compared to a 450/400 .470 has 37.5% more bullet surface area which translates to more effectiveness when dealing with dangerous game.
BTW, a tuskless or a non-trophy elephant in Zim is less expensive (though not by much) than a buffalo hunt and definitely less expensive than even a CBL lion hunt in RSA. Also, there are times when one can find deals at Camp Fire areas on elephants. One area had a lot of crop raiders still left on permit (late season) and I was offered additional elephants at $3K per elephant. A hell of a deal!!!