I could only endorse a 243 on elk if used in an open meadow where one could observe the critter after the shot, but only then with a premium of some sort. The 6mm's don't leave much if any blood and will generally walk off after being hit. I'm not saying a 243 can't be used to knock-off elk but I believe it's, if not unethical, pretty stupid to use one in the timber.
On a friends ranch I watched his 16 year old son shoot a cow at 150 yards with a 100 gr. Hornaday. He hit her broadside through the lungs. She didn't react, but trotted off with another cow. 600 yards later she still hadn't tipped... she was dropped with a 7mm Wby.
