ΔE 24.0, loose: different enough that you should pick on purpose. Bismark's Grave is noticeably lighter, much more muted, cooler than Gothic Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Bismark's Grave is noticeably lighter, much more muted, cooler than Gothic Blue.
The same difference applies the other way round: Gothic Blue is noticeably darker, much more saturated, warmer.
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 Gothic Blue on the colour wheel See Bismark's Grave on the colour wheel
All matches: Gothic Blue equivalents · Bismark's Grave equivalents