People regularly hunt elk with 243s.
This has been my observation as well.
Professional Guides may require a certain caliber due to those they are guiding not being able to shoot and want their clients to have a little margin for error.
For example, I want to go on a guided hunt where the minimum caliber allowed is .375H&H. That's fine, and I would accomodate the Guide's desires, but I would prefer to use a .338 Magnum.
While the .243 is still with us, I see the 7mm-08 making inroads in to the .243 territory. It seems many newer shooters will select the 7mm-08 over the .243 today, but it's not really much of a step up in my opinion. Of course the ballistic tables only tell one side of the story. I have yet to find a 7mm-08 that is as accurate as a .243, and accuracy counts in my opinion. Bear in mind that it's been over twenty years since I last played with a 7mm-08 and have no desire to repeat the expirience.
Conventional wisdom, be it self defense or hunting, would tell you that a bigger bullet is a better bullet. With that said it's what the shooter can shoot accurately that is most important. "A hit with a 9mm is better than a miss with a .44 Magnum."
Guides don't want to track and lose game. I can understand that. That is why they have minimum caliber requirements. The Guide is being asked, or paid rather, to take an unknown quantity, the Hunter, and put them on the selected game animal. What the minimum caliber requirements do is remove some of the variables, IMHO.
.243 is fine for elk if the hunter knows their game, and their range dope, and they are willing to pass on questionable or poor shots offered.
Biker