I think that with lighter bullets (180, 200, 215) the Fed hits harder than it's ballistics would indicate, and definitely harder than the 308.
I think shock factor is the 338 Fed's advantage, at reasonable ranges of course (300 & less)! Personally, I use an 8mm mauser, handloaded
to European specs, and it dumps deer in their tracks, can't wait to try it on Elk & Bear !