Is the main benefit of WSM over Western, velocity?
Shooting higher BC bullets than what's possible with the .270 WSM and its 1:10 twist. There is getting to be a fairly decent list, here are just a few.
Bullets needing 1:9.5-9 twist.
126-141 grain Hammer Hunter and Hunter Tipped165 grain NLRAB Bullets needing 1:8 or faster.
148-162 grain Hammer Hunter and Hunter Tipped175 grain STGK 170 grain Berger EOL 155 grain Barnes LRX