What's more important.....

Inside neck diameter

use a ball or mandrel to even out inside neck so it's concentric to the bullet.

Use proper bushings and you won't need to neck turn.

Neck turn if you take out expander balls so your bushing size your necks evenly.

Neck turning is useful if you WANT uniform necks and believe it's key to accuracy.

im not against neck turning but in a no neck turn chamber (gratuitous amount of neck chamber size) all you need is a nice inside neck gripping the bullet and once you fire and release the bullet doesn't matter what the outer neck dimension is doing
 
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Personally, I think the brass makes a big difference. When I did my load work using Lapua brass on my 6.5x47, I tested using both methods, bushing only and bushing with expander ball, and found no difference in accuracy or velocity numbers. I think other types of brass may yield different results due to more inconsistent neck wall thicknesses.