This was discussed in an old thread, but I'm bumping it up again.

I'm shooting a low-light dance performance with 60D in a church tomorrow night. The lights will change during the performance, and I cannot have any preview of what lights will be like. Very high ISO is needed, from 800-3200 probably.

I plan to shoot with a 10-22mm pretty close so there won't be too much focusing with large DOF. Any ideas about exposure strategies? I could use auto ISO, leave aperture open and SS at 40? Or, set Iso at 1600 and change SS and aperture on the fly? Changing setting on thr fly will show on video, but better than a blown-out scene.

Thanks in advance!

don't shoot slow mo
maybe lower your shutter to 30 if you are on a wider lens
otherwise, not sure how to help you, that's a tough one without knowing how dark or how much lights there'll be

I have shot some band performances recently with my T2I. I used the Canon 50mm f1.8 (aka plastic fantastic) for the wide aperture. This narrows the dof unfortunately. And the loss of zoom means more moving around.

So far I have avoided going above. ISO 800 with success. I also set shutter speed to 1/30. I was using a --Z-finder propped against my eye which helped stability.

For changing light conditions on the run I use Auto and tweak with Exposure Compensation.
Results have been quite good.

Roger Shealy recently gave this good advice:

I shoot manual with auto ISO quite frequently to help with changing light conditions. I'm not sure exactly how well it will work with harsh spotlights, but generally speaking you can set shutter on whatever speed you want, set ISO at 200, point camera to what you feel is the lightest scene you will encounter, set aperture at best setting that scene, then engage auto ISO. You can obviously lock exposure, if desired, or if not, the ISO will adjust to higher ISO for dark scenes and lower ISO for lighter scenes. By calibrating ISO at 200, this allows you one stop lower ISO should you encounter a scene slightly lighter than anticipated. You can increase to a higher ISO during the setup of aperture if you desire more latitude.

http://www.dvinfo.net/forum/canon-eos-60d-rebel-t2i-eos-550d-hd/478247-t2i-auto-manual.html