ΔE 7.8, close: similar, with a visible difference side by side. Fenrisian Grey is a little darker, warmer than Air Superiority Blue FS 35450.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Fenrisian Grey is a little darker, warmer than Air Superiority Blue FS 35450.
The same difference applies the other way round: Air Superiority Blue FS 35450 is a little lighter, 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 Air Superiority Blue FS 35450 on the colour wheel See Fenrisian Grey on the colour wheel
All matches: Air Superiority Blue FS 35450 equivalents · Fenrisian Grey equivalents