ΔE 23.9, loose: different enough that you should pick on purpose. Copper is a little darker, more muted, warmer than Gehenna's Gold.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Copper is a little darker, more muted, warmer than Gehenna's Gold.
The same difference applies the other way round: Gehenna's Gold is a little lighter, 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 Copper on the colour wheel
All matches: Gehenna's Gold equivalents · Copper equivalents