Atmosphere samples can do well in scenes like this from 32 to 64, though some might vary in their opinions about what works best. I like higher numbers here.
Cloud samples are an area I still am learning, since I have not used the Detail settings and need to understand it better. Back when I used the Samples setting, I would never go below 128 and never higher than about 384 for Cumulus. Once I used 512, but only once. The cloud samples (Detail) increases will skyrocket the render times.
I could be wrong, since I can't see the clouds all that well due to the fuzziness of the atmosphere, but you might not need to change your cloud settings.