The 300 WSM is be used by more bullet manufacturers now to test the heavier bullets because of its inherit accuracy. From what I remember, Nosler is using 308 Win for 150 and below and 300 WSM for 165's on up. They are also using the 338 L for 338 batch testing over the 338 WM/RUM.

The question is how far do you plan on shooting. Once the 308 Win goes subsonic 850-1000 (depending on barrel length) you might as well be throwing rocks. That is where the 30-06 and mags come into play.