The 270 Winchester, 7mm-08, 308 Winchester, 6.5X55, etc... will all kill elk very effectively. I have taken 5 with my .270 and 1 with a 7mm Rem mag. My father uses a 7mm Rem mag, my brother uses a .308 Win, one friend that shares the camp uses a TC encore pistol chambered in 7mm-08 and another uses a 30-06. The dead elk have never noticed the difference between these cartridges. The vast majority havve been one shot kills with jsut a few getting a follow up shot just because it the opportunity for one was offered but wasn't needed.

Use a good bullet like a Barnes, Nosler partition, TBBC, Accubond, etc... etc..., put it where it is suppose to go and you will be fine with any of those cartridges you listed out to about 300 yards.

Of course a 30-06, 300 mag, 338 mag etc... will allow you to take stronger quartering shots and still get through muscle, bones, liver, etc... but if you are scared of the gun it isn't going to do you a darn bit of good to use it.