All of of these were jpegs, straight out of the camera, set to "Standard Picture Style" and "Standard" High ISO Noise Reduction.
(I shoot both RAW and jpegs at the same time)
The first image was taken at night where I forgot to change the settings from earlier in the evening, and it is at ISO 25,600
The 2nd image was at ISO 20000
The third image was at ISO 6400
The bottom one could have benefited from a higher ISO, but I had it limited in the camera to ISO 25600
IMAGE LINK: https://flic.kr/p/LK5PvC
108_0461
by
Mark A. photo
, on Flickr
IMAGE LINK: https://flic.kr/p/MGwuq2
108_0459
by
Mark A. photo
, on Flickr
IMAGE LINK: https://flic.kr/p/MZdufq
110_0581_2
by
Mark A. photo
, on Flickr
IMAGE LINK: https://flic.kr/p/NX9nnv
110_0771_2
by
Mark A. photo
, on Flickr
I am very happy with the high ISO performance of this camera.
Answering your question, I usually set a minimum shutter speed that I can get by with when hand-holding, and let the ISO adjust itself to that, but limiting it to ISO 25600.
I attended a seminar once where the instructor stated that it is easier to fix digital noise than fix motion blur (and camera shake), and I suppose he was correct.
I hope that this helps.
(There is a bit more info on Flickr about the images, and there is one to the right of all but the veteran with the flag, that had noise reduction applied in LR5)