ΔE 27.2, loose: different enough that you should pick on purpose. Fire Red is a little darker, more muted, warmer than Doomfire Magenta. They are different kinds of paint: Citadel Doomfire Magenta is a one-coat contrast-style paint and Reaper Fire Red 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 27). Fire Red is a little darker, more muted, warmer than Doomfire Magenta. They are different kinds of paint.
The same difference applies the other way round: Doomfire Magenta is a little lighter, more saturated, 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 Doomfire Magenta on the colour wheel See Fire Red on the colour wheel
All matches: Doomfire Magenta equivalents · Fire Red equivalents