Hope this helps some people.
1) Turn off ray tracing in the atmosphere
2) Use Oshyan's key & fill light setup (attached) instead of relying on the default global illumination rendering.
Delete the lights in the scene.. import Oshyans clip via File->Insert Clip File. Then go to the render settings and set both GI
values to 0.
Ray-tracing in the atmosphere is off by default, fortunately. Not enabling it unless needed is the best approach. It's really only necessary right now for fixing the "sun shining through terrain" problem.
- Oshyan