When we sling these phrases about barrel twist rates remember benchrest rifles have 1-14 and 1-15 twist rates . Projectile length dictates necessary twist rate . The verge of instability generally proves the be the most accurate. Just my two cents
Yes I agree with on the length
When I made the Choice on the barrel I looked at many factors
1.)Bullet being used (Hornady VMax varmint 55g)
2.)Bullet bearing surface length
3.)Overall bullet length
4.)Does it have a boat tail
5.)Bullet nose design (Pointed tip, full metal jacket, flat nose)
6.)Bullet weight
7.)Farthest distance going to shoot (500 yards)
8.)Ogive area radius
9.)Length of barrel to achieve maximum FPS bullet is designed for
10.)Twist rate of barrel for bullet design
So looking at all the information on the 55g VMAX varmint I decided to go with a 24 inch barrel to achieve maximum FPS and to go with a 1/9 twist rate. This way if I ever have to go with a heavier or a lighter bullet I can with the 1/9 twist. But I doubt I will because the Hornady VMax 55g varmints shoot very very well in my rifle.
I know a couple of people who shoot centerfire Competition with a .223 1/14 twist rate, with a 26" Barrel, they shoot 40g hand loads with Excellent results at 100, 200, 300 yards.