Hmmm...a little bit late, I guess...anyway:
Over at Highend3D, you'll find some shaders to render out a separate z-depth pass. Maya's z-depth is 8-bit only, so it comes out aliased. With the mentioned shaders, you'll be able to render the depth info ito 16 bit image files.
Subdivide and conquer!
Free your mind, and your ass will follow!