On one of the "Blain and buckshot" threads on the Big Game forum, somebody listed penetration data from different calibers from tests conducted by (I think it was) Alaska Fish and Wildlife (?). In this test the rounds were fired at some sort of sawdust mixture and the .30-06 outperformed the 300 WM for penetration. And there were numerous other rounds ranked ahead of the 300WM, the two calibers really weren't even close in the rankings.