ΔE 18.5, loose: different enough that you should pick on purpose. Bright Slate Grey is noticeably lighter, more saturated than Basilicanum Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Bright Slate Grey is noticeably lighter, more saturated than Basilicanum Grey.
The same difference applies the other way round: Basilicanum Grey is noticeably darker, 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.
See Basilicanum Grey on the colour wheel See Bright Slate Grey on the colour wheel
All matches: Basilicanum Grey equivalents · Bright Slate Grey equivalents