Hi @DavidJones
Ultimately, you will be more of an expert of the requirements of your intended output than anyone else here. Look to resources dedicated to that output for what will realistically be required.
Theoretically, though, if working with high enough mesh and texture resolution, there shouldn’t be much difference.
Click to read tips--condensed for readability
There are two main components to consider–the resolution of your mesh, and the resolution of your image texture. Both need enough resolution to support the other. Polypainting on a mesh without enough polygons to support the intended detail, or baking that polypaint to an image texture without enough pixels dedicated to that mesh area, will both result in blurry detail. To a lesser extent, the actual tools involved can sometimes be inadequate. If painting with alphas or textures, make sure those images themselves have enough resolution to make clean lines on the target surface.
However, with extreme resolution requirements, it can sometimes be tricky to comfortably get enough polygons or pixels to the areas that require them. This is going to come down to your skill with UV layout and topological discipline (deliberately constructing topology to deliver more polygons to high detail areas when subdivided and fewer in areas that dont require them.) Topological quality is also a concern. As with most things in Zbrush, evenly distributed quads as close to square-shaped as possible will return the best results. Haphazard or stretched topology will produce poor results.
In certain situations it can sometimes be useful to bypass polypaint, and paint directly onto an applied texture instead. Tools like ZAppLink can be useful here. It will allow color to be painted directly onto the texture in an image editor, with the resolution of the texture and your UV layout being the only limiting factors on detail. The applied texture will have the same amount of detail no matter if the underlying mesh is 100 polygons or 1 million. The drawback to this is it limits you to working on a single “view” at a time, rather than being able to paint in real time. However, an eyeball with mostly forward facing detail would be a good candidate for this.
