This is why you shoot f/1.4 primes. IO Echo opening for Bloc Party at the Pageant on their 2013 tour.
It's for images like this where primes reign supreme. During IO Echo's opening set in support of Bloc Party, the stage lighting was extremely dim. Both of these images were shot at 1/80 second at f/1.4 and ISO 5000 with the Nikon D800. I'd originally started out with the Nikon 24-70mm f/2.8 screwed on, but the frame was almost literally black using that 2-stops slower lens and any reasonable shutter speed.
Sure, you could make an equivalent exposure by dropping the shutter speed to 1/20 second at f/2.8 or quadrupling the camera sensitivity. But when you have a couple of f/1.4 primes on hand, that's the obvious choice.
Now, these sample images probably raise the questions “Why are you shooting in horrible lighting?” and “Just because you can make a proper exposure out of a dark scene, should you?” But I'll leave those for another post.