ΔE 6.6, close: similar, with a visible difference side by side. Dark Rust is a little darker, cooler than Oak Brown.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Dark Rust is a little darker, cooler than Oak Brown.
The same difference applies the other way round: Oak Brown is a little lighter, 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 Oak Brown on the colour wheel See Dark Rust on the colour wheel
All matches: Oak Brown equivalents · Dark Rust equivalents