ΔE 6.1, close: similar, with a visible difference side by side. Medium Brown is a little lighter, cooler than Brown 3606.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). Medium Brown is a little lighter, cooler than Brown 3606.
The same difference applies the other way round: Brown 3606 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 Brown 3606 on the colour wheel See Medium Brown on the colour wheel
All matches: Brown 3606 equivalents · Medium Brown equivalents