If you are hunting the plains game in Namibia, then a decent .30 caliber will do nicely.
I recommend a low power scope, with iron sights to back it up.
My scope was a 3-9X, but I shot it a 3X for everything in the bush.
I turned it up to 9X while assassinating Hyrax ("rock rabbits") on rocks WAAAY out there.
I just went with a .308 that belonged to my host. (but would have preferred my beloved 30-06)
I shot Kudu and Warthog with 165 grain bullets. They all died. Longest shot I made on Warthog was about 300 yards. Shortest shot I made was 156 yards for my first Kudu.
My host lives and hunts there, he shot a .300 win mag Remington Sendero with GREAT success.
He did a fantastic 358 yard head shot on a Kudu bull, uphill at a 40 degree angle no less.
Kudu and Oryx are about the same size as Arizona elk, and die with about the same amount of kinetic energy being imparted to their frames, or so it would seem.
The other hunters I spoke to, all African native Afrikaaners, loved the 30-06 and the .338 Win Mag for everything short of Buf.
Buf and Elephant are scarse and EXPENSIVE to hunt in Namibia, even when you consider the current and still plummeting 7:1 exchange rate on the Namibian Dollar.
Namibia, especially in the northern bush, is overrun with leopards. They are less expensive to hunt (than Buf at ~$5K each and jumbo at ~$10K) at about $2,000.00 US each.
this translates to $14,000.00 Namibian!
They take a lot of preparation to bag, so the price is higher than you would expect, considering their numbers.