The best I can get M855 out of a 1:12 is at about 85-90 yards, then it goes south.
Velocity does matter. The test I posted was M16's, A1&A2s.
I have both and my rifles pretty much shot the same report as the test I posted.
Having said that, I have Remington M700 with a 1:12. It shoots the 62s much better then my SP1 (1:12). I'm sure that is do to velocity.
How ever I have a Remington Action Mann Device which is 1:7. Its only an 18 inch barrel yet it shoots the 62s much better then the M700 1:12 even with less velocity.
One must understand that Barrel Twist Guides, are just that, Guides, not all guns are the same.
What I take from John's charts, as well as the Army's, is that fast twist shoot light bullets better then slow twist shoot heavy bullets.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071