The .30-06 and .270 will do fine for elk, but since you will probably be putting a lot of money into this hunt, go with either of the magnums. Pick bullet sizes of 160-175 for the 7mm, or 180 for the .300. Choose a premium bullet, such as the Partition, A-Frame, Barnes X, etc. Just find the one that you can shoot the best and are most comfortable with. And good luck.