Use your 50 f1.4. I shoot local bands using a D300 and the 50 with the aperture wide open, ISO 1600, on aperture priority. Depending on the lighting you'll get widely varying shutter speeds. I don't use a flash because it affects the colors you see from the light show, but I wouldn't argue against taking shots with and without flash.

I'm assuming you can move around. With a D300 you may have to stand quite a bit back from the stage to get the whole band in with the 50, and a wider lens (for example 35mm) might be nice. But I just use the 50 and find I can zoom with my feet, standing back to get the whole band in, and moving to the stage to get shots of the individuals.

If the venue has its own light show you may be able to any of your lenses and get shots when the lights are brighter, but f1.4 surely is nice in dark venues. If you take lots of photos and delete the bad ones, you'll end up with a few nice ones to show the band.

I shoot sports too, and you'll find you can get away with much slower shutter speeds shooting bands, so don't think you need 1/320 to get good shots.

Randy