I shot another modern dance performance in the same place as before when I had no cameras (waiting for my 580 to be fixed and A99 to be delivered) and used a Canon Rebel T2i instead.
The experience was of course much different. I did have a second photographer using a Canon EOS Kiss X3, shooting at the other edge of the stage as we were not allowed to cross the stage.
We both shot mostly in ISO 3200. I used the 50mm 1.4 lens, and Alon used a 50mm 1.8 lens. If you've ever been to a low budget performance in Israel, you'd know that they light the stage very little. They say it gives more character and drama to the shows.
Personally I think they should always have proper back lighting so we would not be forced to use these high ISO settings. Of course the lower-end Canon camera produced more grainy photos.