ΔE 11.6, fair: the same colour family, but not a straight swap. Warpfiend Grey is more saturated, warmer than Strong Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Warpfiend Grey is more saturated, warmer than Strong Grey.
The same difference applies the other way round: Strong Grey is more muted, cooler.
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 Strong Grey on the colour wheel See Warpfiend Grey on the colour wheel
All matches: Strong Grey equivalents · Warpfiend Grey equivalents