[Routine]

The Codex: Chaos Daemons Lash of Despair is a ranged weapon with the Strength: User. Would this mean that a psychic power like Iron Arm or Fiery Form would affect the strength of this attack? Or would it be something like Vector Striking where the strength of the attack is always unmodified?

 

[Nordicus]

Would this mean that a psychic power like Iron Arm or Fiery Form would affect the strength of this attack?

Correct, the lash would get full benefit of any modifier to the models STR. So Ironarm + Lash = Deadly anti-air.

 

[Mossy Toes]

Precisely that. There's some debate in the community as to which is more effective: getting the guaranteed Lash+Psychic Shriek, for dual anti-infantry (which only requires ML1, so is 50 points cheaper to boot), or getting Lash and then shooting with ML3 for the 50% chance at rolling up Iron Arm, which makes the DP so much tougher and makes Lash perfect for killing flyer vehicles.