I do a lot of workshops, and one of them is devoted to ultrazoom digital cameras. Therefore, I own more than a few of the ultrazooms. IS is a very valuable feature, especially in an ultrazoom.
Can you tell us a bit more about your desire to shoot in existing light without flash. Here is a Sony H-5 sample photo. It was taken using stage lighting only and ISO 400.
Here is another sample using existing light and no flash with a Panasonic FZ-7 at ISO 200.