Re: opinions welcomed
If it was me I would talk to a gunsmith and a person from Nosler/ berger/ sierra to verrify my choice. I would lean towards a 10 twist in a wby mag so I could shoot the heavier bullets when needed.
basically you need a faster twist barrel to stablize longer projectiles. Berger's website will give you the recomended twist for their bullets.
however, keep in mind that a 180 grain partition or flat based bullet will stableize in a slower twist barrel than a 180 vld. The LENGTH of the bullet is the factor that we should be concerned with. I have an 11 twist on my tikka and from what I understand a 208 is about the longest bullet I can reasonably stablize. If you go to an ultra fast twist you may have problems shooting ultra light short bullets. but I highly doubt that you will ever notice anything if you intend to shoot anything above 150 grain and go w/ a 10 twist.
Now, If you were talking about a 22-250 improved and a 7 twist barrel to shoo the 90 gr vld bullets... good luck trying to fire a 40 grain pill out of it. as the bullet gets lighter, the bullet will naturally get pushed faster in the same rifle. I cant' remember what the critical RPM's that certain bullets will hande is, but think about it... if you have the choice from a 7" twist or a 14" twist the bullets RPM's will DOUBLE. you can not hardly "overstablize" a bullet, but you can spin it to the point of flying apart. However, when you start to shoot the really heavy bullets, speed will reduce some, and with the faster twist the RPM's will stay within reasonable limits.
back to the 30 cal question... most rifles are chambered in from 10-12 twist. I think that some guys here have built the (forgive me for bringing it up agian) 300 varminter a WSM build around a 110 or 125 grain bullet. I think I've seen 1-15 twist written down. This would be good for that rifle because you are pushing a light jacketed bullet at great speeds so you don't want to stress it more than you have to thus you would like a slower twist barrel. BUTT with the slow twist barrel you will NOT ever stablize a heavier hunting bullet.
A guy from Sierra told me over the phone a couple years ago when I was going through the same problem in a potential build... (something to the affect of the following in quotes)"as long as you are not shooting the lightest bullets you shouldn't have to worry about having too fast of a spin on your barrel as long as you stay within reason"
Sorry for the long reply but if it was me I would get a barrel set for the throat of the bullet you intend to use and a twist rate that will have room for a heavier bullet if you so choose.
I would also look at shooting heavier bullets however (200-220g weights imho- plenty of power to utilize the potential of these higher BC bullets)
sorry for the long and winded post... apparently I am procrastinating so I don't have to clean the garage lol!
I used to re-load but now I "hand-load".
-- Well, at least I try