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...well lit auditorium and no flash is allowed. Dance involves lot sequence of arm and leg movements some time very fast.
The most important factors will be the same as with your 40D: a fast, sharp lens; proper use of shutter speed (slow to impart a sense of motion versus fast to freeze action); the lowest ISO setting that will allow proper exposure at the shutter speed and aperture you're using; etc.
I'm finding that the myriad details of all the functions on my 7D, compared to the few on my 20D, are sometimes getting in the way of my shooting, and so I tend to set things up as simply and basically as I can: no Auto Lighting Optimizer, no automatic focus-point selection, no Safety Shift, etc. This may differ from what works for others, but Manual mode with simple metering settings works for me.