I was messing around in Kaiapoi this evening and was interested to see what high ISO looked like on my D800, I took a few shots hand held at ISO 6400 (still at f/5 and only 1/40s or so), not particularly great photographs but interesting to see the results with different noise reduction applied.
No noise reduction
Lightroom noise reduction (around 37)
Define 2.0 default values
The original really didn’t seem too bad even at ISO 6400.