I don't think his site is online right now, but Campbell Barton (of the Blender Python community) has a mesh decimation script which is concerned with triangulation.  One point on which his script seems to spent a lot of time is the question of triangulating so as to avoid "narrow" triangles.  A quad could be split along either of two axes, and in his case, at least, splitting in the way that avoids long/thin tris is apparently important.  I wonder whether that would be the case here, as well.

Triangulating will potentially double the number of polys to loop through, but it will also enable the (presumed) speed gains of using Numeric and it will reduce the number of edges in most of the in-bounds checks.  Hopefully these points will offset the increase in sheer number somewhat....

With triangulation in mind, I'll go ahead and prepare a version of the script to implement Numeric.  I have assumed we'll just need to to run a "virtual" mesh triangulation before running the lists.  Why will more prep-lists be needed?   

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Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.