When to break t19 2 piece?

[Combustive]

As per title, still using the Nighthold 2 piece bonus (5% increased chance to activate arcane missiles) Ask Mr Robot still recommends this set currently and my sims show it still pulling ahead- using an 900ilvl Shoulder and 890 Cloak . When does it become worth it to break this set? I got an 960 Cloak from my weekly chest this week and it still sims lower despite offering almost 1000 more intellect.

[magictricks]

you think thats bad, i got t19 cape and shoulder both at 925, i can't replace them until i have Mythic t21.

[Waterballs]

I swapped it for t21 2pc HC and I simmed 30-40k more, not a great swap but an increase all the same.