All good advice given so far but I will tend to side with bigger is better for elk. I carry a 338 usually. I have seen 270, 30-06 and a alot of in between take elk. Elk are tough critters. Shot placement and bullet selection are king for elk.

The .270 has killed its fair share of elk. And it is capable to still do so. The other two rounds that you have mentioned are not that different from the .270 that you have now, so I dont think buying one of those would be a solution to your dilema. If you where thinking about adding another rifle to your gun cabinet that is suitable for elk I would choose one with a larger bullet diameter. I would think something in the 30 caliber or larger range. lets say .300 win mag up to the .338 win mag. I am a huge advocate for the 30-06, I think it's a great "all around" rifle. It has done it all from medium sized game to grizzlies. But because of the simple fact you already have a .270; a 30-06 would not be that noticably different performance wise and only offers a larger bullet. Most of the time the 270 and 30-06 perform very similar Thats why I would probally think closer to the .338 if you were looking for a noticable difference. This is just my opinion though