Hi.
Even with the lowest settings (which prevent a crash) at some point in a flight > 45/60 minutes the clouds disappear, together with all trees, buildings, roads etc.. All that is left is the Sun, a blueish sky + (diminished) landtextures.
i7 980x @3.45Ghz, 18 GB DDR3 RAM, GTX780 6GB VRAM, 500 GB SSD