ΔE 3.9, very close: most people won’t see a difference side by side. Polished Silver is a little darker than Grey Knights Steel.
Can I use Polished Silver instead of Grey Knights Steel?
Yes, for most jobs. Very close match (ΔE 4). Polished Silver is a little darker than Grey Knights Steel.
Can I use Grey Knights Steel instead of Polished Silver?
The same difference applies the other way round: Grey Knights 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.