Ardent,
Maybe so, but a .308 is a heck of a sheep rifle compared to a .32-20
Maybe it's just me, but the dude is saying that he's totally comfortable and confident with his .308 out to 600 yards. Do we really need the added range of the .300? If a bullet sent from the .308 goes through the lungs at 600 yards, it's game over. And if the wind is bad enough to rule out a shot with the .308, the .300 ain't gonna save the day.
Just ran the numbers through JBM using the atmospheric variables where I do most of my shooting:
Using the 168gr A-Max, 10mph crosswind, at 600 yards:
.308 2750fps - 26.6" drift
.300WM 3200fps - 21.4" drift
An extra 5" of drift at 600 yards isn't enough to dissuade me from packing the lighter, handier rifle up the mountain. To me, when I'm climbing mountains looking for sheep, it's all about the rifle. The weight, the bullet, and the shooter's confidence with a particular rifle, are important factors. Chamberings are a distant consideration (within reason).