ORIGINAL: Alsatian
I think the assessment of these two cartridges would have to be the Weatherby .257 magnum is faster and hence flatter than the .25-06, which are general advantages of the Weatherby over the .25-06; and the Weatherby .257 magnum has more kick, a louder report, is more expensive using either off-the-shelf or handloads, and is generally more difficult to find if you happen to forget your ammunition on the coffee table at home and have to resupply at some out-of-the-way feed store in Lone Wolf, Wyoming, which are generally disadvantages of the Weatherby against the .25-06.
I own a .25-06 and love it. Every deer I have shot with it went down in a big hurry. For me, the discussion above would push me to prefer the .25-06 to the Weatherby .257 magnum, but if someone gave me an accurate .257 Weatherby magnum I would be happy to shoot it and use it! One thing I have realized about myself is that I should keep my shots under 300 yards, and few people would argue a .25-06 shooting 117 grain bullets isn't flat enough out to 300 yards to reliably take antelope or deer. What does a Weatherby .257 magnum buy me if I keep my shots inside of 300 yards? More expensive ammunition, less flexibility.
Or even within 400 yards for the 25-06. It is a legitimate 400 yard gun on deer, sheep, etc. I tend to agree, why make more noise, kick, expense, etc. when there is no need? It is why the .308 and the 30-06 get sighted in then stay in the closet all season while I am out with the 25-06. I use game ear or special ear plugs or whatever with all of them, but the 25-06 is the only one that doesn't make my ears ring if I don't have hearing protection (lost an ear plug then had to shoot at a deer). Maybe the 26 inch barrel?