Blademan,
I would experiment with the different high ISO settings. I personally don't use auto iso, but if I did, I would limit it to 1600 or 3200 tops on your camera. I've gotten very nice shots at 6400 ISO on my Nikon D3s and D800 but you will notice degradation starting around 1600. You certainly dont want to allow the camera to use the entire range out to 25600 as those shots will have lots of grain and far less detail and color saturation. You should go to dpreview.com, find your camera and look at the images under different ISO. Then you can make an informed decision about the upper limit to set on ISO. Everything on digital cameras are a tradeoff. Yes you can shoot in the dark without flash, but the photos will lack fine detail and the color will be washed out.