Great question, no real definite answer IMO.
If the animal in question, elk, is perfectly broadside within the give range; I hardly doubt it will notice.
Further out, gotta look at projected impact velocity. The ELDX is around 1800fps IIRC so use that as reference point. The ELDM will expand at a little lower velocity but may not hold as well together on off angle shots.
In my 300PRC, I have killed 9 animals with both the factory loaded 212 ELDX and 225 ELDM from 120m to 891m in the last 2 seasons. Two animals (both mule deer) required a follow up shot each due to my error. One using the ELDX and the other ELDM. Two elk, one cow and one spike both on cull hunts were bang/flop using the ELDM; around 380m.
So my sample base is pretty small and not using the same bullet or weight.
There's a few threads here some while back on ELDX/ELDM performance that are informational reads.