The question is not weather a .270 will kill an elk it will. The question is how far do you want to pack the elk. I have shot several elk with a .308 Win. and killed them dead But usually had to carry them a long ways.
You will not always knock an elk down with the first shot. Even when I use my .375 H&H I have had to track them.
Most important thing is shot placement. Most any thing over 24 cal. will kill an elk but be prepared to track them after the shooting.
Good luck on your hunt.
Exblaster