The above is one outfitter's opinion.
Then I read this from the Alaska Department Fish & Game.
"Most experienced guides prefer that a hunter come to camp with a .270 or .30-06 rifle they can shoot well rather than a shiny new magnum that has been fired just enough to get sighted-in. If you are going to hunt brown bear on the Alaska Peninsula or Kodiak Island, a .30-06 loaded with 200- or 220-grain Nosler® or similar premium bullet will do the job with good shot placement.
Only consider using a .300, .338 or larger magnum if you can shoot it as well as you can the .30-06."
http://www.adfg.alaska.gov/index.cfm?adfg=hunting.firearms