Timbo,
I have to agree with d-a on the 1-8". Although I don't have a 6.5x284, one of my shooting buddies has one with the 1-9" twist and can definately see a slight difference in accuracy when going from the 120 to 140gr bullets. His shoots the 120gr Nosler Ballistic Tip like nobodies business, but shoots the 140/142gr pills around .75-1". Probably "gud enuf" for most people but not for him. He wanted to shoot the 140's at LR (1000yds) but doesn't feel confident enough with it. He now has a cryo'd 28" Lilja 6.5mm blank with 1-8" twist. He hasn't screwed it on yet but plans to shortly. Hope this helps. Johnny K.