ΔE 42.9, loose: different enough that you should pick on purpose. Metallic Green is noticeably lighter, much more saturated, cooler than Dark Emerald.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 43). Metallic Green is noticeably lighter, much more saturated, cooler than Dark Emerald.
The same difference applies the other way round: Dark Emerald is noticeably 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 Dark Emerald on the colour wheel See Metallic Green on the colour wheel
All matches: Dark Emerald equivalents · Metallic Green equivalents