I've got a gunsmith friend who has been building 6.5 WSM rifles recently. They're mostly shooting the 130-142 gr bullets right now but it should handle the heavier ones as well. I like the 26 Nosler too. I've done a few barrels for the Desert tactical SRS rifles in that round and it has the room and available components to make the 150 and up size bullets work. I would think if you can get the speed out of it like the WSM, RUM or Nosler should then 1-8 twist would be fine.
Frank
Frank