ΔE 17.6, loose: different enough that you should pick on purpose. Silver Grey is noticeably darker, cooler than Slaanesh Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Silver Grey is noticeably darker, cooler than Slaanesh Grey.
The same difference applies the other way round: Slaanesh Grey is noticeably 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 Slaanesh Grey on the colour wheel See Silver Grey on the colour wheel
All matches: Slaanesh Grey equivalents · Silver Grey equivalents