ΔE 17.4, loose: different enough that you should pick on purpose. Iceberg Grey is a little darker, more muted, warmer than Leviathan Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Iceberg Grey is a little darker, more muted, warmer than Leviathan Blue.
The same difference applies the other way round: Leviathan Blue is a little lighter, more saturated, cooler.
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 Leviathan Blue on the colour wheel See Iceberg Grey on the colour wheel
All matches: Leviathan Blue equivalents · Iceberg Grey equivalents