First off I am saying that shot placement is by far and away the most important component of building a good elk rifle. Or any other rifle as far as that goes. I have been around hunting for a long time and as far as Elk cartridges go I would rate the 260 and 6.5x55 at the lower end of my comfort zone. The 7MM-08 and 7x57 Mauser would improve the comfort feeling. The 270, 280 7mm Rem Mag are in the middle of my Ideal zone. The 8x57, 35 Whelen and 338-06 are right in there with a bit heavier bullet. For close range the 35 Remington 44 Mag, 444, 450 and 45-70 can't be beat. All the 300 Mags,338's 8MMags are good elk cartridges but way more than I would ever use( personal Preference) and found from Expierence that I just didn't need to go to although I tried most all of them except for the very new ones. Any of these rifles given a hit through the vitals mean that you will be packing out and eating elk.
Ok right in the middle, Give me the tired old worn out, non exciting, boring, 30-06 and I will be happy. However I wouldn't give up the old Swede either.

The fastest I ever saw an elk go down is one I shot right where the chest and neck join with a 300 grain bullet from a 44 Mag TC contender The shot was about 70 yards and he was walking right at me. Even though I was in plain sight, I don't think he had any idea that I was there. The gun went boom and he was on the ground.