I wuz readin' one time about the designing of the .308, and the term "volumetric efficiency" was mentioned. The .308 is a good bit shorter than the '06, but its velocities aren't all that far behind, for practical purposes. "They say" this is due to better volumetric efficiency of the .308 as compared to the '06. Okay, I'll accept that as rational...
The '06 case lends itself to being sort of a "Baby .375 H&H", in the sense of a .338 or .35 bullet and the length of the case.
I don't think I'm horribly in error to say that the '06 case has a somewhat better volumetric efficiency in .338 or .35 than it does in .30. Well, "sorta", and "It seems to me."
Consider the larger game animals, where deep penetration, breaking of heavier bones, and probability of exit wounds is more difficult than with the typical white tail deer, the heavier .338 and .35 bullets make sense.
No, I've never had one, but every now and then I've mumbled about the Whelen, anyhow...
, Art