Well, I think we've about exhausted the subject. What it really comes down to is shot placement. If one can put a bullet in the right place it really doesn't much matter how large or small, light or heavy, long or short, fast or slow the bullet may be, they all kill. That presumes of course, that the bullet has penetration adequate to reach the vitals. It is a fact that some bullets can be driven into the vitals from angles that would be impossible for some other bullets. I've not taken elk with the .243 but I'd not hesitate to do so if the opportunity arose. However, I'd take only broadside chest shots with the .243, whereas a 30/06 would be able to take advantage of some shots I'd have to pass up with the .243.
The long and short of it is "anything will work if used within the limits of its' capabilities".