@Henry: I changed atmo quality to 64, and it's better now. I have to be very careful though with what I all put in, as it's a very heavy burden for my cpu/memory. Without preallocating memory, it crashed yesterday. With allocating it rendered fine at 2000px wide. There are maybe 60-70 objects plus one pop of trees. And I need to make this a big one (5000px wide). I hope it'll work out. I repainted all the image maps, with a tiny edge of snow at the wall bases.
@Domdib: You're right, I have to do that.