The .308win is used in sniper rifles, first by military snipers, because of the weight of the rounds. You could carry more ammo for the same weight, or the same ammo for less weight...and the difference in trajectory was small enough that the portage issue was worthy...LE agencies picked up their sniper rifles from military suppliers, until it became popular enough that they didn't HAVE to buy them this way...there are several arguements that the .308 is a better "sniper round" than the .30-06, short action vs. long, lighter recoil, lighter rounds, less powder, same effective range....and I'm sure I'm forgetting a great deal...Of course, there are at least three other (4 total) common "sniper" rounds used today, even within the same regiments and by the same snipers, the .223 in the accurized M-16, the .308 in accurized M-14's and 40X's (and other bolt rifles), the .338Lapua, typically in an AR-30, and the .50BMG in the AR-50 (military version).

If I'm not mistaken, the weatherby is considered to be the flattest shooting, which is occasionally incorrect. Flatness of trajectory, assuming the same bullet is used, is dependant upon one thing, velocity...the faster a cartridge can push it out there, the less it falls per x number of feet traveled horizontally...the weatherby is typically the fastest, with MANY rounds very close behind, but not many that people are familiar with (lazzeroni, patriot, dakota, even the RUM and WM/WSM). Occasionally, the weatherby gets passed up in certain guns/loads by other rounds, maybe not all the time, but it does happen in specific scenarios.

However, with the .300/.308mags, you're paying for the SLIGHTLY flatter trajectory, and paying dearly. As far as the effective range for most hunters, there's nothing you can do with a .30-378 that can't be done just as well with a .308 (they've both typically got ample power at any given range to get the job done, but you're not likely to get either of them on target past 1000yrds anyway!!!) but the faster/flatter the round, the more it kicks (with the same bullet weight/type), the .308 is one of the most shootable rounds you'll ever handle, while the .30-378 is getting uncomfortable for even the most seasoned of shooters.

A great trade off, probably the most efficient "hyper .30" in my opinion, is the .30-06 Ackley Improved...outstanding "wildcat", considerably more potent than the .30-06, but not much more hard recoiling.