Second "silly" question...
Agreed. Definitely should use ISO1600 or above. The trade off of noise for less blur is more than worth it under this situation. Also agreed that it's better to shot at f/2.0 or even slightly smaller aperture. Not just for sharpness but also the shalow DOF at f/1.8 may not be satisfactory. You want some DOF for concert scene.
My 20D produces excellent pictures at ISO 1600, Rachel. And, for
concert situations, I don't hesitate to use ISO 3200. With 3200, I
use Noise Ninja to reduce the "grain."
I've gotten some pretty decent concert pictures at 1/60 second and
f/5.6 when spotlights were on the stage. My 70-300mm DO lens is
image stabilized; so 1/60 is a practical shutter speed with it.
The 50mm lens on the 20D is the equivalent of an 80mm lens on a
full-frame digital camera and should be pretty useful close to the
stage. Instead of using the full f/1.8, I'd shoot at f/2.0. The
improvement in image quality with the lens stopped down a bit
probably will be much more useful than the extra half-stop or so of