ΔE 21.1, loose: different enough that you should pick on purpose. Iridescent Purple/Green is noticeably lighter, more saturated than Ironbreaker. They are different kinds of paint: Citadel Ironbreaker is a metallic and Tamiya Iridescent Purple/Green 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 21). Iridescent Purple/Green is noticeably lighter, more saturated than Ironbreaker. They are different kinds of paint.
The same difference applies the other way round: Ironbreaker is noticeably darker, more muted.
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 Iridescent Purple/Green on the colour wheel
All matches: Ironbreaker equivalents · Iridescent Purple/Green equivalents