N> Some math whizzes

[Namine]

When you have exactly 90 total dex, including buffs and other gears but excluding that one single accessory slot, then Iara and Zerom do the same thing for cast time.

Iara is better than Zerom when your total dex (again, including buffs and other gears) is lower than 90. The moment your total dex is higher than 90, then Zerom is better.

I don't feel like typing out a page of calculations as proof, so you'll have to just trust my word on it.

EDIT: this is only true if you have no other cast reduction (or cast increase) gears like Robe of Cast. If you do, or if you have a 2nd Iara, this actually breaks apart... the equation will have 2 unknown variable (total dex excluding zerom, total cast reduction excluding Iara) and get exponentially complicated. So I did the easy case only.