Here is a Vue 6i scene I did using MSFS-X, with an older MegaScenery still screen dump and using that still as a backdrop inside Vue (rather than compositing). The clouds were done in Vue. I ended up rendering layers anyway, so I might just as well have done a composite.

http://www.renderosity.com/mod/gallery/index.php?image_id=1450902

The MSFS-X scene was done by flying over an area that looked like what I wanted, near Bakersfield California, and setting the instrument panel (in 2D panel display mode) to be transparent ("W" on keyboard). Did the background motion blur in Photoshop.