Ironbreaker vs Mica Silver

How close are they?

ΔE 25.0, loose: different enough that you should pick on purpose. Mica Silver is noticeably lighter, more muted than Ironbreaker.

Can I use Mica Silver instead of Ironbreaker?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Mica Silver is noticeably lighter, more muted than Ironbreaker.

Can I use Ironbreaker instead of Mica Silver?

The same difference applies the other way round: Ironbreaker is noticeably darker, more saturated.

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.