Re: 260 Rem.
Most factory twist are 1-9. I think some building custom rigs even go with 1-8" twist for the 140/142gn bullets. I bought my youngest son a Rem 700 LSS Mountain Rifle in .260 Rem about 7-8yrs ago. He and I "shifted ownership" of a couple of rifles during the Christmas holidays. I let him hold my .25-06 Sendero and he left me the .260 Mtn Rifle. I just finished reloading some 100gn Partitions for it about an hour ago. Will try them tomorrow if the weather breaks.
If it were me building a custom rig, I go with 1-8" and at least 26" long barrel. Some may say different. JohnnyK.