ΔE 7.2, close: similar, with a visible difference side by side. Imperial Purple is a little lighter, more saturated than Magecast Magenta.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Imperial Purple is a little lighter, more saturated than Magecast Magenta.
The same difference applies the other way round: Magecast Magenta is a little darker, more muted.
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 Magecast Magenta on the colour wheel See Imperial Purple on the colour wheel
All matches: Magecast Magenta equivalents · Imperial Purple equivalents