Interesting about the '06 not being enough for Eland. Lately, I've watched a video, twice, of a chap shooting an Eland with a 350gr. FN cast bullet from a German Company's rifle called an "Umarex" Hammer .50 cal.(rifle made in the USA). The Eland walked slowly, kind of in a 1/2 circle, maybe 25 to 30yds and dropped dead.
That rifle is an air rifle, developing about 870fps muzzle vel. & producing about 866fpe.
Impressed I was, so I bought one. LOL - fun to shoot and actually recoils(but not much)