I have been hunting elk since I was a very young man and I have used the 270 with great success. I have hunted elk and guided elk hunters for over 35 years. I have never found ANY need to go to a larger caliber.
Not to say I have not killed many of them with bigger guns, but mostly because where I hunt there are also a lot of grizzlies.
So have no fear at all. Your 270 is just fine.
I would agree that a 150 or 160 grain bullet that will hold its weight is best.