I didn't state that very clearly in my last post. I was trying to point out that I'd rather have a stable bullet at 2200fps than an unstable one at 4200fps.

Of course, muzzle velocity is directly linked to rotational velocity (RPM's) by the twist rate. My point was that it's much better to have a muzzle velocity that properly stabilizes the bullet weight I'm using than to just maximize my muzzle velocity.

I might be able to gain 100fps by using a 1 in 12" twist instead of a 1 in 8" twist, but a 1 in 12" won't stabilize a .223rem 68grn bullet nearly as well as a 1 in 8"... So even though the 1 in 12" barrel might need a little less dope, it isn't worth anything if my group opens up from 3/4" to 2".

Like you said, it's possible for a guy to bump up the power charge just a bit to use a heavier bullet in a slower twist, or to back off the powder to slow down a lighter bullet in a faster twist, but it really only works for a bullet weight that's on the fringe of your twist rate, meaning a guy might be able to push a 77grn bullet hard enough to stabilize well in a 1 in 12" .223, but it's not going to let a guy run a 90grn Berger. You're right, it's a little iffy, it works for a little ways, but at the end of the day, I don't like to depend on my powder charge (read chamber pressure) to make up for a poor choice of bullet weight for my barrel.

All the stars have to allign: powder charge, chamber pressure, bullet weight, muzzle velocity, caliber, barrel length, and twist rate all need to be in sequence to make it work, and as you well know, even when those stars all allign, all of the stars in the neighboring galaxy need to allign, and then all of the stars in the galaxy across the street have to allign too... These are just the short list to find a starting point, and beyond that is usually experience, skill, and a little luck, not just calculation.