Re: Bullet weights and Twist Rates
JLA provided the best info. Appropriate twist rate is really about how long a projectile is, but most bullets are differentiated depending on what weight they are. More weight = longer bullet. The length of your barrel with have an impact on the muzzle velocity of the departing projectile (longer barrel = longer push from gas pressure = higher velocity), but won't really make a difference in accuracy.
I can tell you from my own experience that your 1-in-12" .223 will be best around 55 grain and lower. the 1-in-9" .223 should be quite versatile from 45 grain all the way up to the high 60 grain range. I know some people who have shot 77 grain in a 1-in-9" with great accuracy, and others who started to see spreading groups. All depends on your barrel, and you won't really know what will work until you try it.
Just out of curiosity, are the barrels steel, stainless, or chrome lined?
I can't really comment on the .30-06 from first hand experience, but I'm sure others will be able to (or Google).
Knowing is half the battle...
Of course, the other half is violence.