Being that an eland is the size of an Alaskan moose, I'd be a bit hesitant to purposefully go after one with a .243 regardless of which bullet I used...and I say that as a stout and devoted supporter of .22 CFs on deer; even big mule deer.
I'd start to feel comfortable with a stout 130 grain .277" bullet, but would take a .300 Mag of some sort in your hypothetical situation. As for a bullet, I'd love to whack one with a 200 grain original Speer grand slam (the best bullet ever made for game IMO), but an A-Frame, accubond, Interbond, TBBC or even a partition would be where I would really start to feel comfortable.
