You change the prefs to allow it to use more memory and subdivide the mesh more, I can get to about 20-30 million per mesh off the top of my ehad, think thats the limit I've got to.
Also use sub tools to get more polys etc.
But yeah I thnk Z's only 32 bit. was hoping that they might bring a 64 bit version out but dunno.
"No pressure, no diamonds" Thomas Carlyle