So... I've noticed that the CPU isn't used very much when exporting using GPU (AMD APP) ...
this leads me to think that it would be possible to export 2 files in parallel - one on the GPU and one on CPU.
So i'd like to submit a feature request of parallel export.
Alternatively you could speed up exporting by mixing these two techniques... export 1/2 using GPU and 1/2 using CPU
either way - exporting could go a lot faster by utilizing GPU and CPU simultaneously.