That's why round-nosed bullet often shoot more accurately than pointed bullets of the same weight.
I think you have that backwards. The pointed bullets will be longer then the round nose bullets of the same weight.
Look in any reloading manual that shows the ballistic coefficient of the same cal. bullets. The pointed bullets are longer and have a better BC.
As to the twist recommendations for 223s. Why limit your self. The faster twist will shot lighter bullets as well as heavy bullets. The slower twist will only shoot lighter bullets.
The 1:12 is good to 55 grains, The 1:9 64-69 (if you're lucky), the 1:7 is good to 90 grns.
This chart from an Army Manual will explain what I mean.