Short answer, go to each bullet mfg web site. Some will list the min twist for each of their bullets. EG, Berger shows their 6mm 95gn Hybrid to work with 1:9. Their 105gn says 1:8 twist is minimum.
Long answer.
The mfg rating is not the final word. For example, my 1:9 twist .223 barrel did just fine with 77gn SMK's even though the box clearly stated that a 1:8 twist was required.
Bullet stability is a multi-faceted issue. Bullet design, length, tip, and weight all combine with the rifles twist rate and muzzle velocity to determine if it will be stable or not. External affects can also apply. A combination that works on a hot summer day may not work on a cold winter day since the air density is different.
Typically a shorter bullet will have better stability, but, then the drag will be higher than a longer bullet at the same weight.
The only way to know for sure is to try some.
As for caliber choice, I went with a 6BR for informal range shooting out to 1000yd. It has a 1:8 twist barrel and typical muzzle vel is 2800-2900fps. 103gn Vapor Trail and 105gn Bergers both work well. 108gn Hornady do not. Yep, that little bit of difference is important. Whatever you choose make sure the barrel will stabilize the bullets you want to use. Recently the bullet mfgs have been making heavier bullets in calibers so a barrel made for something like the 6.5CM might come with a twist made for bullets like the 140gn, and not stabilize the new 153gn Hornady or 156gn Bergers.
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