Here is proof that shader GC produces identical results to render GC, provided that you have been careful about the configuration of the lights.

I am using one infinite white light at 95%, and a procedural IBL that has been carefully set up so that the amount of light it produces is the same with or without render GC enabled.

In this render, I'm using shader GC on the figure's skin, but not the eyes, or the chair, or the ground.

---

Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)