How close to the stage/artists were you? I have shot several concerts at ISO 400 and 800 with no problems, using the kit lens, the 70-210 f/4, and a sigma 400 5.6. I am typically on the stage or first row though.
Usually I set my flash on rear curtain, and -1 to - 1 1/2 stops. Almost any of the 2.8 lenses should be good quality, as they typically are along the top of the line from any given manufacturer.
Could you post an example and perhaps EXIF so we may be able to provide more help?