ΔE 23.2, loose: different enough that you should pick on purpose. Payne’s Grey Wash is cooler than Agrax Earthshade.
Can I use Payne’s Grey Wash instead of Agrax Earthshade?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Payne’s Grey Wash is cooler than Agrax Earthshade.
Can I use Agrax Earthshade instead of Payne’s Grey Wash?
The same difference applies the other way round: Agrax Earthshade is 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.