If elks on the agenda at longer ranges, the sensible choice is the 300 WSM with a good 180g bullet such as the AB. It will get the job done out there a ways.
If mostly for deer, the 270 WSM is a great performer with 140g bullets at long range. I was pushing 140's at 3250fps with magpro. That makes for a very excellent LR deer medicine. Loaded with a good 150g partition at 3100fps, it will still take its fair share of elk out to at least 600 yards, giving good shot placement. I would not feel undergunned what so ever.
The choice is yours, both will do what you want easily to 600 yards up to elk, the 300 WSM will just be alittle more insurance.