Good discussion. I'm thinking here, if the light is low, why not just take advantage of that and go for a creative long exposure shot? I think it would look cool to show the motion of the people in the mosh pit, and the band members too. With plenty of trials, there's a decent chance you can come up with something that would work. If you can brace the camera somewhere (or bring a really small tripod), a 1-second exposure could produce some fun results. Who knows?