I've taken elk with the 270 WSM, 7mm Mashburn, 300 Win Mag, 338 Win, and 35 Whelen. They've all worked great for me. I've seen smaller work well and would use my 6.5x55 or similar without to much worry. I just like rifles so it's probably more about the rifle than the cartridge for me.
I do have a lot of confidence in my 7mm Mashburn Super and my 338 Win. Both have just been with me when I've had to make a couple tougher shots but I'm sure a 270 would've worked about the same.
