ΔE 25.0, loose: different enough that you should pick on purpose. Fire Opal is a little darker, much more muted, warmer than Gehenna's Gold.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Fire Opal is a little darker, much more muted, warmer than Gehenna's Gold.
The same difference applies the other way round: Gehenna's Gold is a little lighter, much more saturated, cooler.
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 Fire Opal on the colour wheel
All matches: Gehenna's Gold equivalents · Fire Opal equivalents