So you can see how some of my builds and recommendations work in practice:
I'm "Unfit" in this Warzone. "Fentanyl" was deemed an inappropriate drug reference. I'm planning on appealing that decision. Until then? I'll enjoy the fruits of gearing up and using relics/adrenals. I have 317 Expertise (7% damage increase).
And in the Warzone right after:
(In case you don't know what's after Invincible, it's Immortal.)
Screenshots (click for full size images) taken by Sands, since my hand's still broken. I'll have to take a picture of my cast later -- yes, 400k damage in a full hand cast while playing lying down on a couch. That takes a lot of practice.
My build: Marksmanship (31/7/3).
Happy New Year!