You mean based on this one? I’m currently trying to setup something similar (kind of a not so uber uber-material :)), and the thing that has caused me greatest issues are the combination of metallicness and variably tinted specular as one affects the other (in my setup anyway, but I’m pretty noob in Blender/Cycles). I don’t have access to their software, so for me it’s guesswork trying to figure out if and how various sliders are interlinked. I’m also using translucency (with tint control towards base) as kind of a replacement for SSS (I need mine to be GPU friendly), but metals don’t have any transparent properties, so that caused some additional issues.
What do you mean “The glossy component is GGX with roughness linear roughness, squared”? I currently use Beckman for metallicness and GGX for specular, and will probably use Beckman for topcoat as well (not there yet). I use fresnel node for specular, but only blend value for metallicness. In my setup, at full metallicness, I have no specular mixed in at all (as its grazing angles will always be white and not realistic to pure metals).
One trick I always do is to significantly darken the diffuse component of metals, even if its contribution is very low. That way I can add additional base gloss to a diffuse component (low amounts, so the metallic colorization won’t be noticeable), or simulate very rough metals by using a tad of low intensity diffuse at the bottom, freeing up the metallic glossiness to produce narrower highlights while having it bright enough to produce desired effect. For me, a material is either metallic or dielectric, so their approach of allowing 50% metallicness sounds silly to me. 10-20% or 80-90%, maybe (metallic impurity and so on).
I operate in groups; “Diffuse or Metallic” (also handles translucency), “Specular”, “Sheen” (not fully in yet), and “Clearcoat” (not in yet but should be easy). In the two main groups, a lot of pipes go in to vary effects that shouldn’t need to be, but I am using Mix Shaders for everything so far. I’m arguing with myself if Add Shaders controlling what goes into it at the end (to maintain energy levels) would be a better approach. I’m not sure.
I can post screenshots of where I’m currently at (I’ve ruined everything a couple of times already :D), but it’s just too messy at the moment. I’ll keep this thread in mind if I ever finish it.