everything I've read says to get the most out of the 257 you need a 26".
MAYBE...
possibly probably, but definite maybe...
Every rifle (and ammo combination) is a unique individual. Many are very similar, but some are much different from the average.
"getting the most" from a round usually means the highest velocity that still gives the desired accuracy.
And longer barrels USUALLY give higher velocities. But not ALWAYS. Some barrels are "faster" than others, and a "fast" barrel can deliver velocities greater than a longer "slower" one. And a "fast barrel might be faster with everything, or might only be faster with certain bullets and loads. Individals, each behaving in its own way.
IF you don't already have one, get a chronograph. Using a chronograph, comparisons between different rifles and identical ones can be eye-opening.
I have personally seen 100fps difference in average velocity between 3 guns with the same barrel length shooting the same ammunition. Not common, but it does happen.
A good friend of mine loved his .270 Wby (26") because of the speed he was getting, compared to his .270 Win (22"). UNTIL he got a chronograph, and discovered that his .270Win was actually a handful of FPS FASTER than the longer barreled Weatherby!
He either had a fast Win or a slow Wby, maybe even both. Its not common, but it does happen.
A barrel isn't worn out until you decide it is. That's one thing to a match shooter and something else to a deer hunter. One big thing that shortens barrel life (even in non magnum calibers) is HEAT. Rapid fire, hot barrel, steel erodes faster (more erosion per round). Not likely to be a real issue with a Weatherby bolt action but something you should be aware of.
Not sure about today but in the old days, 3-5000 rounds of deer level accuracy was the expected standard of barrel life for standard rounds, overbore rounds shooting slow powders usually gave less, sometimes considerably less. Lots and lots of variables at work.
One thing you might consider, is getting your next barrel now, or in the near future and just storing it until you need it. If they are stored properly, they don't spoil.