I agree on needs above 6400 iso.
My needs for high iso are really wildlife only. When landscape shooting I will have a tripod, and the only time I can remember using higher iso settings is when I am working on a windy day and I need to stop motion of trees.
Wildlife, (Arkansas, Oklahoma, Texas) my main areas, tend to be early morning, or late afternoon shots. Never (should never say never) bright day shots. Here I am working in a blind or field and action has can be quite fast. Moving large animals in low light can be tough but also very rewarding. My solution has been to use a cheaper lens, example Canon 100-400 which won't give me the best 400mm=F6.3 so I am forced into the iso 1200, 1600, 2000 range very fast. The point I was trying to make, in the past with Canon and the 5d MKII getting something worth printing at iso 2000 @ F6.3 could be hard. With the D800 at 1600 to 2000 I am finding I tend to get very good results. Much cleaner files and the DX mode comes in very handy.
My other frequent addiction is to work birds, small and medium and again either in a tree or blind. In a tree working fast and not wanting to carry the larger glass. In a blind, the larger glass is usually fine. However it's very rare to have "great" light as if you do, the birds are not coming in. Mixed light tends to be the case. Here again I am quickly using iso 800 to 2000 to both get the shot and have a fast enough shutter speed to stop the motion.
The D800's iso range works great in this style of shooting. A real plus is that you are still at around 15mp in DX mode so you have a lot of resolution to work with.
The point I was trying to make is that you will be surprised by just how good the D800 in the mid to high iso range can be. It's actually pretty amazing considering it's a 36mp sensor.
Paul