ΔE 12.0, fair: the same colour family, but not a straight swap. Iridescent Bright Gold (Fine) is noticeably lighter than Gehenna's Gold. They are different kinds of paint: Citadel Gehenna's Gold is a metallic and Golden Iridescent Bright Gold (Fine) is a pearl paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Iridescent Bright Gold (Fine) is noticeably lighter than Gehenna's Gold. They are different kinds of paint.
The same difference applies the other way round: Gehenna's Gold is noticeably darker.
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 Gehenna's Gold on the colour wheel See Iridescent Bright Gold (Fine) on the colour wheel
All matches: Gehenna's Gold equivalents · Iridescent Bright Gold (Fine) equivalents