I have cleanly taken the game you listed with a .280. There is not much difference between a .270 and a .280 with a 150 grain pill.
Usually a .30-06 is my light rifle in Africa but the .280 works just as well. The only reason I take the .30-06 is that it is a common cartridge nearly everywhere and the .280 is not. The .270 is a very common plains game cartridge in most places.
I have run into people that think the minimum legal caliber in Namibia is 7mm. That is wrong. The 7mm is the recommended minimum caliber by the guides association but it is not a law, as the real law only requires minimum energy levels. It might be easier to carry a 7mm or larger just to avoid explaining this to people. Sometimes people are thick headed.
