Totally agree with Mark, except for one thing: Shoot one test roll, cut the roll into thirds, develop one section at at time at the chosen times. Why burn two or three rolls, when you can get the test done with one? (Unless of course you are going to shoot the test rolls at different ISOs, but then you're probably complicating things. I would bet that the on stage lighting, with a decent fast lens, is going to be pretty strong already. You might not have to go as far as 1600.