I'd get a used entry level Merkel in .500 and use the leftover cash for extra trophy fees or Taxidermy. Spending an extra 8-12K on a rifle isn't going to make the rifle mean more to you after you've taken a few elephant and buffalo with it. After the safari, it's all gonna be about the animals taken with the rifle, not the engraving or wood quality or maker's name.

JMHO,

John