IsaoShi explained everything correctly. You cannot compare a render with a GC shader without taking into account that you have too much light in your scene.

This is a very complex subject, but I hope this helps.

Few people seem to realize WHY they add so much light to the scene, or why it is so hard to keep the lighting looking good if you move anything.

The reason is that adding lights, particularly IBL, decreases the perceived produced by looking at a linear render on your sRGB computer screen.

Here is an example. I have here a few props. Those on the left are not gamma corrected. Those on the right are gamma corrected. The non-GC props look pretty good, because I've used a 60% white IBL and a 40% infinite light. That's a LOT of light. A real-life scene would NEVER have that much light coming from all directions. But to keep the non-GC objects from looking strange, Poser users add lots of lights and set them really high.

The GC props look over-lit, and they are!

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