In my recent findings while I was trying out a workflow where I texture my highpoly with ptex and then bake it down to lowpoly which is suppose to create seamless high quality textures. Problem was it was too error prone and time consuming when it comes to baking inside Mudbox.
Polypainting in zbrush seems to be a more viable option since it stores the diffuse into the vertex color which can be baked in Xnormals. Ptex pretty much is only useful for movie Vfx. Until Mudbox get a better algorithm or method for baking Normal maps and Color maps, it will be inefficient to use Ptex in a game pipeline. I have wasted enough time trying to get this method to work lol.