My build PoB links:

https://pobb.in/99yy2LDLhi7e

https://maxroll.gg/poe/pob/6x4yo70u

Gem gives 5% (6% at lv4) chance to gain Soul Eater stacks on kill,

When you're playing a mapper, farming late game content, it's basically always up.

At 45 stacks of Soul Eater, this gives 225% increased Attack and Cast speed -

Faster Casting Gem at lv 40 gives 54%.