I had a 3 groove 1:14 twist 35 Whelen rebore Jesse did a while back, pretty sure that's what he seems to prefer to do. It shot into 1/2" or better with ammo it liked, from 200gr hornadys to 225 accubonds to various 250gr bullets. I ran it out to 400 yards with the 225 accubonds and they were still flying well at that distance.
In short, 1:14 or 1:12 would both work fine, though I'd lean toward the 1:12. I seriously doubt you will see a difference unless you end up running the heavier A-frames or heavier (310gr ) woodleighs. It's also possible that the 1:12 does a better job of stabilizing the 225 accubonds, which are pretty damn long. I have run those out to 750 yards from my 1:12. They make tiny groups at that distance as long as the wind is calm.
