I prefer the 270 but have used the 257 Wby and would have no issues in using it day in and day out for elk.
If one builds they can do a nice light 257 Wby, but other than building there isn't a lot of lighterweight options. If I had to do a 257 Wby I'd grab a 700 and wrap a Ti take off around it. Then it'd have the weight out front that I like and would still be fairly lightweight.
Bottom line, either round is fine with me as long as I can get it in a rifle I like to shoot and carry.
Dober
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"the 25/06 is merely a .270 that took a week off from working out-what one does the other can do with the same effort".....Royce