ΔE 18.1, loose: different enough that you should pick on purpose. Gold Brown is a little darker, much more saturated than Iridescent Gold Deep (Fine). They are different kinds of paint: Golden Iridescent Gold Deep (Fine) is a pearl paint and Vallejo Gold Brown is a metallic, 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 18). Gold Brown is a little darker, much more saturated than Iridescent Gold Deep (Fine). They are different kinds of paint.
The same difference applies the other way round: Iridescent Gold Deep (Fine) is a little lighter, much 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 Iridescent Gold Deep (Fine) on the colour wheel See Gold Brown on the colour wheel
All matches: Iridescent Gold Deep (Fine) equivalents · Gold Brown equivalents