My first elk was with a 338 WM... I'd read all the gun-rags (pre-internet) and had concluded elk were nearly armor-plated.
After killing a couple with the 338 WM, I decided they were indeed flesh and blood and I might as well carry a lighter rifle that I enjoyed shooting, so my elk rifle evolution (or devolution depending) started.
I'm currently sitting quite satisfied with the 308 Win as my primary elk rifle. I'd be equally happy with a 270 Win.
I see no need for anything heavier or harder kicking...