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