Since the difference created by GI is being questioned, I did another pair.

The scene has the Abrams tank, the ground, a pyramid, and the environment sphere. On the EnvSphere, I have a panoramic image. I have one infinite light for the sun.

This render is done in Poser 8, but using IBL instead of IDL. 

IBL = Image Based Light
IDL = Indirect Diffuse Light

These are completely different techniques attempting to accomplish the same goal - to simulate the "ambience" created by light bouncing off one surface and illuminating another. IBL is fast and for many images is a big improvement, but only in comparison to NOT doing anything whatsoever about ambience.

Now keep in mind, this image is using Poser 8 HSV Exponential tone mapping, so that we don't have gamma correction problems. If you were rendering in Poser 7, you'd have to do more work just to match this; either using GC or HSVE shaders, or doing postwork. So even though I'm not using IDL yet, this is already a better render than you could get from Poser 7 in a straightforward way.

Note the insufficient shadowing under the Abrams. If I were to crank up the AO enough I could darken that, but then upper areas would over-darken. You can already see some excessive AO on the side of the tank.

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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)