I think you should consider your body build when picking a 6.5 Grendel for shooting different positions. I find that I swing the 16" barrels better than the longer tubes but I'm getting older, not as strong with shorter arms for my height. I have a friend who has gorilla lenght arms and he can easily shoot 20"-24" rifles with long stocks easily.
The 6.5 Grendel is fully capable to deliver good accuracy out to 600 yards with a 16"-18" barrel. If I were interested in a good accurate barrel in your situation I would call Precision Firearms, JP or Lilja. If your a newer shooter, trigger time will make a huge difference and you might consider a 16"-18" barrel from AA. Spend the money you saved buying a cheaper barrel on ammo and learn to shoot beyond that barrels capability. Then invest in a cut rifled barrel from a top quality manufacturer.
For twist I would go 1:8 twist for 18"-24" or faster twist 1:7.5" for a 14 1/2"-16" barrel.
The 6.5 Grendel is fully capable to deliver good accuracy out to 600 yards with a 16"-18" barrel. If I were interested in a good accurate barrel in your situation I would call Precision Firearms, JP or Lilja. If your a newer shooter, trigger time will make a huge difference and you might consider a 16"-18" barrel from AA. Spend the money you saved buying a cheaper barrel on ammo and learn to shoot beyond that barrels capability. Then invest in a cut rifled barrel from a top quality manufacturer.
For twist I would go 1:8 twist for 18"-24" or faster twist 1:7.5" for a 14 1/2"-16" barrel.