ΔE 18.7, loose: different enough that you should pick on purpose. Grey Blue is noticeably darker, much more saturated than Iron Man.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Grey Blue is noticeably darker, much more saturated than Iron Man.
The same difference applies the other way round: Iron Man is noticeably lighter, much 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 Iron Man on the colour wheel See Grey Blue on the colour wheel
All matches: Iron Man equivalents · Grey Blue equivalents