ΔE 8.9, close: similar, with a visible difference side by side. Sycorax Bronze is a little lighter than Rusty Brass.
Can I use Sycorax Bronze instead of Rusty Brass?
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Sycorax Bronze is a little lighter than Rusty Brass.
Can I use Rusty Brass instead of Sycorax Bronze?
The same difference applies the other way round: Rusty Brass is a little darker.
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.