ΔE 35.1, loose: different enough that you should pick on purpose. Permanent Violet Dark is noticeably darker, more muted, cooler than Impish Rouge.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 35). Permanent Violet Dark is noticeably darker, more muted, cooler than Impish Rouge.
The same difference applies the other way round: Impish Rouge is noticeably lighter, more saturated, 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 Impish Rouge on the colour wheel See Permanent Violet Dark on the colour wheel
All matches: Impish Rouge equivalents · Permanent Violet Dark equivalents