If you do get an opportunity for Africa, by all means TAKE IT!!!!
Great place and not really as expensive as you think especially compared to a nice elk hunt, etc in NA.
But, you don't need the .338 for plains game. Most of it is taken with 30-06 or 270. You can't use it for dangerous game (at least in South Africa). South Africa hunting laws require a .375 minimum for cape buffalo and the other dangerous critters.
BTW, you will see more game in RSA in the first few hours you hunt, than you will see in a lifetime of hunting in NA.