I own, and skied the P50 motion for a few days now. It is based on the P50 Platinum, with brownisher paint, and the integrated rails on which a Marker Titanium 1200 binding slides.
There is one particular characteristic i found on the P50 motion of which i am not sure if you can get it out of the P50 with conventional bindings (or any other ski with conventional bindings (of which i have and demoed many), or in other words, a characteristic which i think is a characteristic of the motion system's rails): I am able to very easily apply edge pressure at the heel/pad level as opposed to just bare foot pressure. I like that a LOT. I do NOT like the fact that i am "married" to the selection of Marker bindings sliding on the rails. The factory-installed Titanium 1200 does not keep up with the performance of the P50. My DIN setting is ca. 7, which works fine for me at the toe piece (comment on that: some folks appearently have problems with boot fit there, resulting in pre-releases and broken metal plates, so make sure you bring your boots when you buy to give that a check), but which is too low in the back when i try to slam-dunk a bump section. The 1200 IMHO is a NoNo for big guys (200lbs+), because they propably do not have the option to crank it up to a sufficient level if they like.