When the materials are set up properly, GC should effect shadowing and highlighting only.

GC for transparency, bump, displacement and gradient bump should be 1, there is a Scripts menu option doing this.

Diffuse + Ambient should be less then 0.8, but the 50% grey establishes this.

Reflections > 0.1 are rare for non-metals, even diamonds don't reach 0.25. And specularity is a form of reflection, so count that one in as well. With this respect, the shader might be tuned a bit.

AO is meant for Diffuse IBL lights only.

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though