And chew on it I will... thanks so much for this, Bagginsbill!! Hope you have a spectacular weekend.

Hoping mine will end up being specular-free...

Just looking at it real quick:

So, material-based GC means turn off renderer GC. Have commented out Bias line. (Interestingly, I was messing with bias and gain when I played with your 2007 version).

Confused about a very basic thing, here... sorry if I'm being a dunce. I though linearising was done with AGC() and correcting was done with GC(). No? So:

linearColorMap = GC(colorMap)

has got me scratching.

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks