wow great start there man!!
I have a couple questions, I am assuming both textured and untextured renders are rendered in Brazil, and that you are using a low res cage mesh w/ a displacement map, if this is true do you feel that you are getting a faithfull representation of your Z sculpt with Brazil rendering via displacement mapping
I ask because I have strived and strived to accuratley reproduce my Z sculpts with displacement maps during rendering and can only seem to get about 90 percent of the way there, I am using Turtle and mental ray for my tests, it seems that on things like legs or other things that are cylindrical with normals all pointing pretty much away from the center it works best, but with a face with lips, nostrils, etc where you have normals faceing each other that it falls apart a little,
seems like you have a really good render, thats why I was wondering if the grey scale was with Zbrush or not/