Out of a 15" barrel, which would you choose and why? Is 1/9" fast enough in the 7mm BR to stabilize heavy bullets? Is there any advantage to a 1/7.5" twist over a 1/8" twist in the 6mm BR? Pure paper punching and rock busting.

Stay with the 6BR and a 7.5 twist. Good velocity, good bullet selection, less recoil with the chance to spot yourself.

Either twist you mentioned will work for pretty much the range of bullets typically used in these cartridges. My 6BR is a 1-8 nad it shoots 107gr bullets fine. I shoot 168gr out of my 7BR. Now if you are wanting to shoot 1000 yards the 6 Dasher would be my choice in 6mm. If you are not set on the BR cases the the 6.5-284 Norma is also an excellent 1000 yard round. I love mine. My 2¢

Bret

For 1K I'd want a little more horsepower than the BR's.

I think the 6 creed will get you there

I love the 6BR and have shot one at 1000 yards at the MOA shoot,it is a 15" 8 twist and it got in the shootoff a few times at the different yardages.I felt it is a bit slow with the 105 class of bullet,Perhaps if I was better at wind reading?@&$
Like I said it is accurate and I love the BR case,but for shooting at that distance I was thinking I should have a little more horsepower.Thinking about a new chambering for Hunter class now
Matt