An experiment that anyone can try, and which only takes a few minutes, is a follows.
Put your favourite lens on you favourite camera. Step outdoors, find a detailed subject, and do a series of exposures at a range of shutter speeds, from silly slow to ultra fast. Use a variable ND filter so that the ISO and aperture remain the same for each shot.
Load the files on your screen and step though them at 100%. You will quickly see what hand-held speeds allow critically sharp images, and which don't.
Add image stabilization, caffeine, and lack of sleep can be added as variables. Season to taste.
You'll be amazed.
I've just done that Michael and the results tend to confirm that a shutter speed of 1/FL in conjunction with VR
is about right, although maybe not as reliable as a faster shutter speed, or the use of a tripod, in producing consistently
However, I don't have a variable ND filter at hand. I used to use those mostly during my waterfall phase a few years ago. In any case, the reality is, when shooting hand-held, one may have to contend with the negative effects of noise and image degradation due to underexposure or use of a higher ISO if the shutter speed requires it.
If the sharper results from a shutter speed faster than 1/FL are negated by greater noise, then so be it. That's reality.
Because memory and storage is now so affordable, I often bracket exposure +/- one stop. The problems I tend to find with the greater exposures which may be close to a 1/FL exposure (in conjunction with VR), is unsharpness due to subject movement rather than camera shake. For this reason I may prefer the least exposure at 4x the shutter speed of the greatest exposure, even though it's far from being an ETTR.
Although I wasn't able to use a variable ND filter for my tests, I was able to use a brick wall as my test target, and a very nice brick wall it is too.
In order not
to appear biased I've included two pairs of comparisons of 100% crops that have received no more than the default sharpening of 25 in ACR.
One comparison shows an exposure at 100th with a 120mm lens being at least
as sharp as the same scene shot at 1/400th, with VR. The other shows an exposure at 1/125th being very slightly less sharp
than another shot at 1/400th. Nevertheless, the 1/400th shot is noticeably noisier, and a slightly greater amount of sharpening applied to the 1/125th shot more or less equalizes both sharpness and noise.
My favourite VR lens at the moment is the Nikkor 24-120/F4. In fact it's my only Nikkor lens with VR, so it has to be my favourite.
I see no reason why the test images below would not be relevant to a D800 situation, the difference being that one would simply get a wider FoV with the D800 at the same focal lengths used.