ΔE 31.3, loose: different enough that you should pick on purpose. Medium Magenta is noticeably lighter, much more saturated, warmer than Kakophoni Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Medium Magenta is noticeably lighter, much more saturated, warmer than Kakophoni Purple.
The same difference applies the other way round: Kakophoni Purple is noticeably darker, much 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 Kakophoni Purple on the colour wheel See Medium Magenta on the colour wheel
All matches: Kakophoni Purple equivalents · Medium Magenta equivalents