[Adamantium]

I'll assume you are talking about 223 Remington. With faster twist rates you get the ability to stabilize longer bullets but may lose the ability to shoot the very lightly constructed varmint bullets (which can tend to tear apart after leaving the barrel). But I've seen people shoot 55 grain FMJ and SP bullets in all twist rates with good results.

There is just a lot more to a good load than the length of the bullet (which is what matters for twist rate, not the weight). So while it can certainly matter if you are wanting to shoot either extreme in bullets, it doesn't always matter. But then again I mostly plink and shoot 3 gun so for me its more about shooting skill than fractions of MOA accuracy difference.