ΔE 8.6, close: similar, with a visible difference side by side. USAF Medium Gray is a little lighter, more saturated than Coldstone Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). USAF Medium Gray is a little lighter, more saturated than Coldstone Grey.
The same difference applies the other way round: Coldstone Grey is a little darker, 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 Coldstone Grey on the colour wheel See USAF Medium Gray on the colour wheel
All matches: Coldstone Grey equivalents · USAF Medium Gray equivalents