That's a really gorgeous cloudscape and nice high-altitude view!
I have some questions about your render settings. When you say "micropoly and AA set to 3", do you mean that micropoly detail was actually at 3, as in 3.0?? If so that's very, very high! I would not recommend more than 0.75 in this scene (and most scenes). And if Defer Atmo is enabled, your cloud and atmosphere quality is going to depend largely on your AA setting.
Also, at this large scale, DoF is going to have no real effect and is essentially not useful.
- Oshyan