Tonedeaf,
I can't claim to be an expert at concerts, by any means. I used to hesitate to go above 400 ISO with my D200. Now, I'll crank it to 1600 and shoot B&W. I'm with Sanjay, you can get better high ISO results using B&W.
But when the club is dark, I've asked permission to use flash. Here's a couple from Snug Harbor on Frenchman St. in New Orleans (which rarely gives you permission to take a picture, much less use a flash!) I attached Gary Fong's Lightsphere II (Cloud) on the SB800. Henry Butler's fingers on the keys.
I shot some of these with a 28mm f/2 but a couple were with the not-very-fast-at-all 18-200VR at f5.6 and 1/50th. All ISO 400 except where noted.
Here's without flash -- longer exposure/movement effect (should have gone 800 ISO!)
You can compare that with a 1600 ISO B&W in a Paris Brasserie...14-24 f2.8 lens @2.8 1/30th
Footnote: I do have a press pass. But when I get the new D700 I'll leave the flash in the bag!