I've never done any "stage shots", but have shot allot with low light ambient only inside. You have the right idea, either the 35mm f/1.4 or the 24mm f/1.4 will do much better than the 24-70. Not so much because they can shoot at f/1.4, because the IQ isn't that good at f/1.4. It is because their IQ is much better than the 24-70 at f/2.8. If you can keep those lenses a bit over f/2.0 they do a very good job.