ΔE 40.7, loose: different enough that you should pick on purpose. Pearl White is noticeably lighter, more muted than Ironbreaker. They are different kinds of paint: Citadel Ironbreaker is a metallic and Tamiya Pearl White is a pearl paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 41). Pearl White is noticeably lighter, more muted than Ironbreaker. They are different kinds of paint.
The same difference applies the other way round: Ironbreaker is noticeably darker, more saturated.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Ironbreaker on the colour wheel See Pearl White on the colour wheel
All matches: Ironbreaker equivalents · Pearl White equivalents