ΔE 34.1, loose: different enough that you should pick on purpose. Space Grey is noticeably darker, much more muted than Frostheart.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 34). Space Grey is noticeably darker, much more muted than Frostheart.
The same difference applies the other way round: Frostheart is noticeably lighter, much 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.
See Frostheart on the colour wheel See Space Grey on the colour wheel
All matches: Frostheart equivalents · Space Grey equivalents