ΔE 7.3, close: similar, with a visible difference side by side. Obsidian Black is a little darker than Dark Steel.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Obsidian Black is a little darker than Dark Steel.
The same difference applies the other way round: Dark Steel is a little lighter.
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 Steel on the colour wheel See Obsidian Black on the colour wheel
All matches: Dark Steel equivalents · Obsidian Black equivalents