ΔE 27.8, loose: different enough that you should pick on purpose. Garnet Purple is noticeably darker, warmer than Magos Purple.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Garnet Purple is noticeably darker, warmer than Magos Purple.
The same difference applies the other way round: Magos Purple is noticeably lighter, 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 Magos Purple on the colour wheel See Garnet Purple on the colour wheel
All matches: Magos Purple equivalents · Garnet Purple equivalents