It’s interesting, because I am using the same geometry with the painted materials, added the clear coat shader to it to the duplicated geometry, and there hasn’t been any of the negative effects I would have expected. No Z fighting or other artifacts.
My shaders are a little messy because of all the experimenting. Eventually I will clean them up and optimize, add parameters for instancing as well.
This first shader is the gloss clear coat, being added to the duplicated mesh. It’s fairly simple with added grunge and orange peel normal map.
This second material is handling two shaders, the base color, and a metallic shader for the paint flake. The individual flakes are being driven by the alpha blend. I was originally going to use this layering technique for the entire shader, but because the clear coat didn’t work out, I think I will condense these three shaders into one material. Although blending two materials into a third makes adjustment simpler, I don’t think it’s worth having all the materials separated.