Their review of the Z2 measured a contrast of 700:1
Their review of the Z3 measured a contrast of 900:1 in cinema mode.
Their review of the Z4 measured a contrast of 1100:1 in cinema mode with the adaptive iris turned off, 1600:1 with the iris turned on.
I don't know what special color filters are and how they achieved 4100:1 contrast, but it appears the D5 panels add about a 20% increase of the D4 and the rest is done with the adaptive iris 'trickery'.
By the way, the Sony HS51 measured an 1200:1 with the iris off
Infocus 4805 - 1800:1