Thank you for this information. Let me ask a few questions by way of clarification:
When you say "the upper limit of predicted performance is 1/500 sec shutter", what exactly do you mean? Do you mean, perhaps, that VR is of no use on shutter speeds above 1/500 sec? I'm guessing, though, that this is not what you mean inasmuch as at shutter speeds above 1/500 sec, one wouldn't need VR anyway.
When you say the "fastest speed that it ought to be able to track is 1/500 but expect better consistency at 1/100 or 1/250 than 1/500", I assume "it" refers to VR, but please correct me if I'm wrong. Also, when you say "track" what are you referring to? What is actually being "tracked" here?
So that you'll know, my concerns here relate to taking portraits, fashion, and glamour shots outdoors with a D600 while the subject is standing still, but the shutter speed, based on light conditions, is too low to guarantee that I can hold the camera perfectly still while the shutter fires. A special concern is that I often use auto focus ("AF") in these shots, locking the focus on the most important part of the subject by depressing the shutter release half way, which, of course, also engages VR, and then recomposing the shot while keeping the shutter release half way down. The big question I have on this is whether once I have the shot recomposed, which frequently involves moving the camera a significant amount, is the VR still engaged such that whatever vibration there may be in the recomposed position (which could be different than the vibration in the original position) is effectively reduced when I take the shot. My shooting results in the field (which frequently reflect a soft focus where the AF was locked) would say "no", but I could be mistaken on this--while I'm inclined to attribute the soft focus to the VR being ineffective in the recomposed position, there could be other problems, e.g. defective sensor or lenses. If the answer is, in fact, "no", then how does one engage VR effectively in the recomposed position without losing the focus lock established before the recomposition took place?
Naturally, I'd welcome your and anyone else's insights on this issue, and many thanks in advance for any help you or others can offer here...