Set it at 1000, go into the mosh pit, meter the palm of your hand and use that exposure directly.
Normal practice when metering your hand is to open up one stop from the reading. Since 1000 is already "over" you can take the palm reading directly.
This has the benefit that you will properly expose the people. I assume that's what you'll be taking pictures of.
If you want to include people on stage, go up on stage yourself and take a meter reading to use for stage shots. (Maybe unrealistic - just take a reading in the spotlight if you can ever get the spot on you. They sometimes aim at the audience).