Well, you've got kind of a muddle of settings here. You have Detail at 2, while a maximum of 1 is usually advised, and less is often more than sufficient (e.g. .75). I suspect you may be using 2 because you've got Raytrace Everything enabled, but in your scene with a heavy emphasis on terrain I would not normally recommend it (though admittedly in another thread I discussed the surprising finding that it did seem to produce better results in a specific scene - I would not generalize this beyond that scene though!). So I would suggest turning off Raytrace Everything for a start, then set detail at 0.75. Set your cloud layers to Quality 1 (ignore the number of samples this sets). Increase your GI, otherwise you're going to get flickering as this does seem to be animated (I would do a Relative Detail of 2 and Sample Quality of 4). Then finally increase your antialiasing since both your atmosphere quality (when Raytrace Atmosphere is enabled) and - perhaps more importantly - your motion blur quality depend on antialiasing samples. An AA of 6 would probably be good. With AA6 you may ultimately be able to reduce some of the cloud and atmosphere samples further to save render time a bit, but keep an eye on noise.
- Oshyan
