Few things to add which may help.
First... look at
http://misfitphotography.co.uk/ - all my shots taken with 7D and 17-50 F2.8 lens. Some are up to ISO6400 and I am simply not concerned about going that high, at all. Noise can be catered for without issue. Just get the exposure right and you are set.
Lighting, I would say see how a few shots at 1/125 F2.8 ISO1600 look and take it from there. I will go to ISO 6400 and down to 1/60th before I will consider using flash (if allowed). If I do get to flash territory I will still run at the above settings, and set flash to about -1 to -2 compensation. Saves batteries and much less of a distraction on the band and the crowd. But try not to use it at all if possible.
External flashguns do have another benefit when the light is low... AF assist beam. I have one of my customer settings on the dial including flash set not to fire, but external af assist ON. This helps greatly when the lights are poor quality...
Without flash I shoot manual, starting at 1/125 F2.8 and auto ISO up to 3200 (higher if needed).
Oh, and don't forget to have fun.