Cadre Grey vs Bastion Grey

How close are they?

ΔE 21.9, loose: different enough that you should pick on purpose. Bastion Grey is noticeably darker, more saturated than Cadre Grey.

Can I use Bastion Grey instead of Cadre Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Bastion Grey is noticeably darker, more saturated than Cadre Grey.

Can I use Cadre Grey instead of Bastion Grey?

The same difference applies the other way round: Cadre Grey is noticeably lighter, more muted.

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.