Elmer: What Guy said + 1.
Put the appropriate weight premium bullet in the "right" spot on Mr. Bull from any reasonable range, and you'll be eating elk steaks for a long time from either of those calibers. My personal choice is the Barnes TTSX (Tipped Triple-Shock) or Nosler Partition or Accubond, but there are others in the same catagory. (These are high BC bullets too)
If you intend to shoot the rifle alot, go with a .308...cheaper more plentiful brass available, better bullet selection, mild recoil, legendary accuracy, more rounds in the magazine, shorter barrel, easier handling in the field.
If you want more range and more power, but with more blast, recoil, more expensive hard to find brass, burn more powder, probably a longer barrel and less rounds in the magazine, well then, the choice is simple. They're both excellent calibers, just suited to different tasks (to me). The 270WSM to me would feel right at home in BC, shooting across some alpine canyon past "normal" .308 ranges (whatever that may mean to you) when a magnum rifle really comes into play. If you really don't need that kind of performance, then the 'standard' caliber should work just fine with proper bullet selection and
shot placement.
Of all the elk I've killed, the longest shot was on a 5x5 bull at 278 yards. I could have made the shot with my .308's easily, but that day I had my M70 .338-06AI....another 'standard' caliber if you will. Makes me wonder how all those elk got killed for over 100 years before magnums got invented......
Okay, off the soapbox.