I'm calling BS on this published load data for the .257wby is faster then the .25-06 and the 24'' barrel compared to the 26'' tube has been proven to only slow loads down by 48fps. Food for thought there are loads using the 100gr barnes tsx in .257wby that cross the chronograph at 3900fps I don't think your .25-06 can even touch that.
The .257wby is an amazing cartridge it can be loaded with 75gr vmax of yotes and 100gr TSX of moose its the one caliber that can do it all. The down side is the ammo cost so reloading might be a future hobby you should look at. The .257wby out preforms the .270 win in all aspects using the same weight bullets and does it with less recoil.
Everybody knows that published data is only a general guide. The published data for 25-06 and 257 Wby. shows significant velocity gains in the Wby.
However, I've loaded a lot for the 25-06 with both a 24" and a 26" bbl.
Here are some admitedly 'apples and oranges' numbers, loads chronographed:
24" bbl. using H4831, Norma MRP (Reloader22) and IMR7828; best I could do without any signs of pressure and never exceeding top publiahed data was 3025 fps with 120 gr. bullets.
26" bbl. using IMR 7828, same 120 gr. bullet, ave. velocity 3280 fps.
That's a pretty significant gain for 2" more bbl. length, but not far out of line according to my experience with the 30-06 and 300 Wby., where significant gains can be made by burning a slower powder in a longer bbl.
**I haven't loaded lighter weight bullets than the 120's for a long time because we don't have varmints where I hunt. 100 grainers would be fine for our little Island blacktails, but the 120 Partitions and Hornadys shoot in the same place and very well, so what the hey.
We're kinda getting a bit off topic here, but it's all fun and the original poster sure doesn't seem to mind.

I still say that given the family connection and negligable cost he should grab the Wby.
Provided of course that he keeps us informed.