ΔE 20.6, loose: different enough that you should pick on purpose. Medium Magenta is a little lighter, cooler than Doomfire Magenta. They are different kinds of paint: Citadel Doomfire Magenta is a one-coat contrast-style paint and Golden Medium Magenta is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Medium Magenta is a little lighter, cooler than Doomfire Magenta. They are different kinds of paint.
The same difference applies the other way round: Doomfire Magenta is a little darker, 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 Medium Magenta on the colour wheel
All matches: Doomfire Magenta equivalents · Medium Magenta equivalents