one of the points here is, that if you want to use your .223 for longer range shooting, you NEED a fast twist to handle the heavier/longer bullets ... the benefit is you still can drive those heavier bullets at good speeds, and get much less wind drift down range - all while burning minuscule amounts of powder ...
I understand this part. Makes sense for shooting at targets. For varmint shooting though, I've not found the heavier bullets to be satisfactory performers.
stepping up to a .22-250 or .243 to drive the heavier bullets comes at more of a cost, literally ...
There is also a cost to using a fast twist .223. I like the performance I get from $12 a box 50 grain SXes or TNTs, or 35-45 grain Hornet bullets. I can't drive those to max speeds with a fast twist, I have to step up to $17 a box NBTs, VMAX, etc. So there is a cost there, too.
and like others have already said, you can drive 40's all the way up to 80's with a 1:8" twist, and not have to worry about over-spinning the bullets and having them not be able to handle the extra RPM's ... I've seen guys with .223AI's that push 40g NBT's and/or Vmax's at nearly 4000 fps and have NO issues with the bullets not being able to handle it ...
See, that's wrong. That implies you're going to use only the stiffly constructed NBT and not the fragile bullets meant for .22 hornet, .222, and so on which are much less expensive. If you want to shoot the expensive bullets, go ahead and use the fast twist, but doing so closes the door to using inexpensive, light weight bullets in the .223. For my use, those are a whole lot more practical than the 60+ grain bullets since those lack terminal performance on varmints.
fast twist is where it's at regardless of what bullet weight you're shooting in the .223/AI ... you just close way too many doors by going slower than a 9" twist with today's bullet & powder selections ... there's no way around that fact.
It depends on which doors are useful to you I guess. I have no earthly use for a long range .223. It doesn't add anything I want. I do have a lot of use for the light weight, lightly constructed, inexpensive bullets which can't be run at full throttle with the quick twist.
We're probably getting off track here. I'm not saying there's no point at all in a .223 with a 1-9 twist, but the original poster said he didn't plan to go over 55 grains in weight. Unless he changes his mind about that, the 1-12 twist is a better choice for him.
Tom