LV4 - Midnight Purple II
LX0 - Midnight Purple III

As from my knowledge, the difference is in the formulation of Pearl Effect

LV4 does not provided the same color changing effect like the LX0

You will most likely see more colors in LX0 as an effect over LV4
As for the purple shading also there is a slight difference I will say LX0 show more purple under shade. Best is to go to your local auto paint shop and ask for a sample done for effect.

However if you only want the darker purple effect over the color changing effect. You can try using the cheaper priced LV4 and apply no more than 2 extra coat to achieve it. Hope it helps even it is a bit late in reply.

the MPIII is a far more extreme flip and has a gold effect to it as well as the other MP flips in it so it if far more distinctive and less subtle in its appearance.