Intersection between closed BREP (3dvoronoi cell) and surface

Hi.

I have a surface (non planar) and a set of points. I need to extract for each point, the portion of surface that's closer to him than any other point.

Since the surface is non planar, i went for 3d voronoi from which i extract a cell for each point. After this i need to compute the intersection between each cell and the surface. 

I tried two approaches: one with "Brep|Brep intersection" and then "Curve splitting", and another with "Split Brep".

The first solution works (below) perfectly but the "Curve splitting" phase can be bloody slow! Sometimes it requires more than 1.5 minutes

The "Split Brep" solution (below) is much faster, but for each cell it returns me TWO surface: the one inside the Voronoi cell and the one outside. These are inside a three with a branch for each curring surface. The problem is than inside the branches, sometimes the first element is the inner surface, sometimes it's the outer.

Is there a way to use "Split Brep" and throw away the outer surfaces?

Do you suggest any other method?

Thank you very much, and sorry for my terminology: i've been using GH for 2 days :/