Here's a more typical example. It may be hard to make out the difference in the shadow on the curtain, but if you zoom the image larger, it is easy to see.

This is with samples=19. Render time = 90 seconds. (No IDL, just IBL+AO)

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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)