In my experience, it depends how close you get to the action - if you're right by the stage, then a G11 will be fine. Here's one I took where I got lucky in terms of being close up
http://www.flickr.com/photos/efsb/4132473576/
The G11 responds similarly to the settings I'd use on a DSLR - ISO 1600 1/60 of a second. I've also used it with a teleconverter off Ebay, which makes it a bit bigger, but OK if you've got a
couple of big pockets...!
Taken from way up in the Gods at Birmingham Symphony hall -
http://www.flickr.com/photos/efsb/4333806891/