I am sure that the 325 WSM would be perfectly adequate to 300 yds.Past that no one should be shooting unless conditions are great and they really feel they can make the shot from previous experience/practice.

I feel that shooting past 300m is possible but feel 450 yds or 50% further is a reasonable limit. Past that your bullet starts falling like a rock ever 50 yards traveled and your trying to hit a 24"chest with a 8 inch certain kill zone.A rifle shooting 2" at 100 would shoot a 9" circle at 450 yds. I suggest a 1-1.25" grouper at 100 yds to qualify for accuracy for long range elk.Along with accuracy you need penetration and the energy to do that. A 338-378 or Lapua would seem to fulfill that criteria.