Quote - The differences still exist after this had been done.

Er...
A) You enable GC in render settings and start the rendering

1. Poser linearizes ("inverse GC") the maps according to the Maps' or overall GC value
2. Poser renders (in linear space)
3. Poser GCs the result

B) You disable GC in render settings and start the rendering

1. Nothing done...
2. Poser renders
3. (GC is not done or done by the materials or manually afterwards)
   So lacking step 1 in B, the result is different...
   Step 3 is of course done at render time in your example, but could be done afterwards, too. That doesn't really matter.