I had to go from motherboard video processor to fly through the clouds. Even with a good although not a great card, I still can't bump map the worst of them in the center of tank island. With bump map off I can stay near 60fps.
Seems like when I first saw the puffy clouds in maybe December, they were much higher and away from the ground detail. When the clouds were high it did not knock the fps down so bad as it does near the ground.