Yes, this has been a very informative thread.  I'm glad you chose to post your difficulties here.  We can all learn something from this.  Well, as a beginniner, I know I can, lol.

The tip about turning up volumetric light quality is very timely.  I recently rendered an image with a volumetric atmo. but something about it just didn't look right. That must have been it!

Also I would like to add:  I enabled "optimize last render pass" which, and I'm paraphrasing, reduces render times by 3X while leaving out miniscule details.  To me the "miniscule details" it left out were a little too obvious and not really worh the time savings of approximately 3hrs.

One more thing I'd like to add is I never use any AA at all on my final render.  Instead I render at least 4 times larger and then downsample.  It seems to save a bit of time and a lot of guesswork.

I may be wrong about this!!!  Like I said.  I'm a beginner.  Maybe someone can verify this.

Thanks.  :)

Edit:  Sorry, I forgot to mention I'm using Vue5ProStudio.  At least until my Vue5Inf. download link arrives.  WooHoo!!  :D

"Simplicity is the ultimate sophistication." Leonardo da Vinci