ΔE 36.9, loose: different enough that you should pick on purpose. Garnet Purple is noticeably darker, much more muted, cooler than Doomfire Magenta.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 37). Garnet Purple is noticeably darker, much more muted, cooler than Doomfire Magenta.
The same difference applies the other way round: Doomfire Magenta is noticeably lighter, much 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 Doomfire Magenta on the colour wheel See Garnet Purple on the colour wheel
All matches: Doomfire Magenta equivalents · Garnet Purple equivalents