My vote would definitely go for the .375 H&H. You can get ammo for it just about anywhere. Like Old Sarge says "one planet, one rifle". It will take anything. I have one built on an Interarms Mark X action. It is the one I want in my hands when & if I ever get to go for buffalo in Africa.

If I was doing it all over again and didn't have the Interarms action I would go with the CZ 550 and a good synthetic stock.