ΔE 6.7, close: similar, with a visible difference side by side. Burnt Umber is a little lighter, more muted, cooler than Dark Rust.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Burnt Umber is a little lighter, more muted, cooler than Dark Rust.
The same difference applies the other way round: Dark Rust is a little darker, more saturated, 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 Rust on the colour wheel See Burnt Umber on the colour wheel
All matches: Dark Rust equivalents · Burnt Umber equivalents