ΔE 8.9, close: similar, with a visible difference side by side. Boreal Green is a little darker, cooler than Sons of Horus Green.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Boreal Green is a little darker, cooler than Sons of Horus Green.
The same difference applies the other way round: Sons of Horus Green is a little lighter, 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 Sons of Horus Green on the colour wheel See Boreal Green on the colour wheel
All matches: Sons of Horus Green equivalents · Boreal Green equivalents