* On the side...
I've noticed extreme differences between renders when cloud layers have used higher that Q=1.
As example(and sorry, I don't even have any temp files to back this up but, I remember clearly as it's a WIP that I often open...), I have a file that uses Q=4 for cloud detail and looks lovely(this cloud layer is used as an atmosphere in itself, at ground level as a haze, and looks terrible at Q=1, the entire scene looks different at Q=1) Could this be the difference in output you're experiencing, Oshyan? I only post because I remember Bob/Markal's file used around 'Q=50' for quality so, it would then give an extremely different output than what you might have tuned it to use in an optimized version...
* All quality settings I refer to here are cloud detail only, not render detail. To clear up any confusion. *