Trex,
To answer your question, try 83 or 84 grs. of IMR-4320 and any good 500 gr. premium bullet for about 2350 FPS..That will lay low anything on this earth or Marrs...and I really like those 300 gr. Woodlighs in the 338 for African use, and if you run into an upset Buff or Lion while hunting plainsgame, just shoot'em..it'll work fine...

I can't think of a better combo for Africa than a .338 Win paired with a 375, 416, 458 or whatever....that covers the field and still keeps you armed for surprises.