ΔE 8.1, close: similar, with a visible difference side by side. Stonewall Grey is a little darker than Great Hall Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Stonewall Grey is a little darker than Great Hall Grey.
The same difference applies the other way round: Great Hall Grey is a little lighter.
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 Great Hall Grey on the colour wheel See Stonewall Grey on the colour wheel
All matches: Great Hall Grey equivalents · Stonewall Grey equivalents