Let's use 223 Rem for the example. 12 twist barrel typically will stabilize up to 55gr bullets, 50gr being better. I know it's the length and not the weight but in general they are proportional.
If that 55gr can be pushed faster, is the 12 twist more likely to stabilize it or does a few hundred fps not matter enough to help?
In an 8 or 9 twist that will stabilize 69-70gr bullets, will a 50-55gr start to suffer? Wouldn't that over spin the bullet to a point that it would become inaccurate?

I’m not the guy to answer your question, but I do shoot a lot of 40 Nosler BTs in my 9 twist rifle, and they will go into a tight group if I’m having a good day. That said, the 65 gr GameKings do just as well. So I suppose I’m saying that I can’t tell the difference...for what that’s worth.

8 is the common compromise between 55-70 -ish. Someone else will write a much longer and more precise reply.

You can learn a lot about Bullet stabilization from the Berger twist rate calculator. https://bergerbullets.com/twist-rate-calculator/

The faster you spin a bullet the faster it will expand when it hits something. You can overspin and get it to come apart with too fas of a twist rate but doubtful in a 223 to get that to happen with twist rates available.

A bullet that is marginally stable on the calculator can shoot good at 100 yards or more and at some point loose its accuracy due to lacking enough spin for stability.

as to over spinning a bullet I am now in the camp of that is hard to do with most bullets and twist rates commonly available. Some bullets like Speer Tnt they caution about velocity and the bullets coming apart anove X speeds and they can no doubt. I have done that a few times with light fragile bullets, but with most bullets you will not see that.

You're a bit off on your bullet length to twist rate. A 1:12 will stabilize over 60 gr bullets. Google search "Lilja twist rate chart" and "Shilen twist rate chart". But to answer your question, you can drive a bullet faster akd overcome lack of twist rate, at least to a point. But, if you want to shoot it long range, it will suffer in stability.

When you over spin a bullet, it can hit with the nose up. And the extreme is that it will spin the jacket off. Versperman Jr. (S & S Precision) was running an agressive twist 6mm, and a bullet a bit too short for the twist. Shot number 3 in a string, and I would see the puff of bullet jacket about 70 yards out, then the core of the bullet land in water 200 yards out.

While were on the topic. I have a Mossberg MVP patrol. 16 in barrel in 223 it uses Ar magazines.. Web says 1-9 twist. I shoot it with a suppressor. I handload 53g Vmax they actually have a higher BC than the 55g. Anyway I'm wanting to shoot a heavier bullet to buck the wind better and hit coyote harder. I'm looking at the 70 g accubond. Does anyone here have the same rifle and shoot the heavier bullets. My main concern is a baffle strike. Doesn't have to be the accubond just ;ooking for a heavier bullet that barrel will stabilize.
Thanks

I would recommend the 60 gr VMax for 16 inch barrel 223

Spin rate vs bullet weight is directly related, For instance a 55 gr. .224 dia. bullet can be stabilized with a 1: 12 twist, where as a .75 gr. .244 dia. will require a 1:8 twist to stabilize it..
This difference in bullet weight vs velocity vs twist rate is relative to bullet length vs flight time to the target. The slower the bullet is traveling (as in a 75 gr.) the more time it has to
to drift. where as the 55 gr. bullet will reach the target sooner therefore has less time to stray.

Ok, I think I got it. A 12 twist 223 barrel will stabilize a 55gr (length) bullet sufficiently but a 12 twist 22-250 would do a better job of stabilizing the same bullet at farther distances.
An 8 twist 223 barrel is better suited for heavier (longer) bullets but would handle the 55gr just fine.
I can't see myself ever using a 40-45gr in a 223, I have a Hornet for that.

I quite possibly could be having a Buzzsaw moment. With the Hornet and the 22-250, I really don't need a 223, do I?

No, you need a 1:8 .223 and you don't really need a .22 Hornet and a .22-250.