grishazzz, what's your budget? If you can afford it and will be in those situations a lot, go all out, go for more reach. (DA*50-135/2.8 or Tammy/Sigma 70-200/2.8)
I'm not a club/stage shooter but I went on a Nine Inch Nails binge this past year, shooting 3 shows for personal momentos, I consistantly found that I needed more reach. I'd recommend, if you can, renting the DA*50-135 and giving it a try. When I shot with the 28-75, I found myself cropping a lot to get the close-ups. But if you aren't needing close-ups then it'll work. I liked using my FA50/1.4 too, I could stop down and get sharper focus but then I was cropping with it too, so....
Row 8 shots with the Tammy, not the sharpest in the shed but I was still working on my technique:
Hope this gives you a little more to think about. Regardless I use the 28-75 a lot and I hope to one day get the DA* 50-135 for myself. Played with it a bit and its a sweet package.