Sounds good, though you have to be careful that there are no anomalies related to overagressive culling.
I made a small change to precompute the rotation of the orbital plane which boosted the framerate from 7.6 to 9.8 frames per second on my laptop . . . not all that impressive, but together with your change and a couple more optimizations, we can probably get the frame rate to 30 frames per second on 1GHz+ processors.
There's some room for optimizing the display of labels which should help as well.
--Chris