Re: 7mm STW twist and bullet ??
Did a quick calculation
7X57 2450 fps with 9 twist = 196,000 rpm
7MM Rem Mag 3000 fps 9 twist = 240,000 rpm
7mm STW 3100 fps 10 twist = 223,000 rpm
Not sure what velocity Berger bases their twist recomendations on, but I would guess it is something less than the velocity you will get from your 7MM STW.
Should be OK , worth a try.