Yea and u need the 20 ias

Nope, only the base attack dmg.
You need the ias, skill, light res to counter the malus from light sunder.

-res on his infi wont apply to your dmg

Anyway that build is suboptimal

3-4x eth upg titan (carry a cube in inv with 3 inside)
Eni
Griffon 15 ias 3 maek jewel
Highlord
Spirit
Raven
10 fcr high mana leech ring with dual resist or @ and single resist
Silkweave boots
Razortail
2 Java 20 ias dual resist mana leech gloves

= infinite mana and life from all the maek/laek while maintaining 68 fcr

It’s 3 skills and those extra pierces will literally make your lightning fury hit twice as much in a lot of cases

There’s a big difference between hitting 1x 50 bolts lightning fury or it piercing 4 times and hitting 5x 50 bolts