What type of band are you doing? I've used my 70-200 2.8 IS on concerts from the pit, but have run into problems with really moving bands, like Gogol Bordello. Not fast enough shutter speeds. I typically got 1/100s at f/2.8 and ISO 800. Obvioiusly, IS doesn't do much if the artists are moving around all the time.
I like close ups more than overall stage photos, so I really look forward to use my new 135mm 2.0L at a festival in two weeks. You should have a f/2.8 lens or lower.