I got my new GT4542LS tripod which has thicker tube diameter than my regular GT3542LS.
I did some slow shutter speed tests with the 200-500mm set at 500mm, lighting a textured subject with a halogen spot and adjusting the light to subject distance to get access to different shutter speeds. I used 1/6s and 1/15s, f/7.1 (I assumed that would be close to the optimum aperture), ISO 800, on the D810. I took series of 3 shots per set of parameters to test the reproducibility of the sharpness. I tried with EFCS on and off at both shutter speeds. These tests were done with VR OFF.
I would say the difference is very subtle, in favour of using EFCS which gave slightly higher sharpness than when using full mechanical shutter. The reproducibility of sharpness with the 200-500mm + GT4542LS (standard collar) was excellent, in contrast with the AF-S 80-400 on my GT3542LS (with Kirk collar). I will next carry out a similar test in subdued daylight to get a feel for what kind of shutter speeds I can safely use with this rig and whether the purchase of a Kirk support system is warranted. It would seem from my initial testing that the reproducibility of sharpness is acceptable at least in the indoor environment with very little air flow.
I tested the image stability using Live view at maximum zoom. With VR off, the image settled in approximately 1 second after tapping the camera. This seemed to be an improvement over using the same lens with the GT3542LS, no doubt thanks to the more rigid tripod. However, I think there is room for improvement in the collar part of the setup. However, after the 1-1.3 second waiting period the image seemed to be very stable. When I then turned VR on, the image started to drift about in a small region in a seemingly random fashion. So, I will definitely keep VR OFF when using this lens on a tripod. On a monopod I was happy with the results with VR on. I think that with appropriate care, it should be possible to get good sharpness in field conditions at slow speeds using this lens and the GT4542LS tripod in a consistent fashion, and EFCS boosts sharpness slightly, giving more confidence to using the lens although I think it would be very hard to spot the difference in a print of "normal" size.
I think both the tripod and the lens even with standard collar represent an improvement to my previous 80-400 AF-S and GT3542LS when it comes to use at slow (or intermediate) shutter speeds and there doesn't seem to be any of the inconsistency that bothered me with the lens that I had before. I also find that the 200-500's AF doesn't cause any noticeable lateral wobble in the image whereas with the 80-400 AF-S, the image shook left and right a bit when the autofocus was active. This problem seemed to cause some indecisiveness on subject AF tracking when photographing birds in flight with the 80-400, and it bothered me personally (OCD). This lateral wobble in the image is absent in the 200-500, suggesting it is built to tighter tolerances for the focus group (or I might have had a less than perfect copy of the 80-400). I look forward to verifying my findings in field conditions outdoors and see how well the setup handles wind. I am cautiously optimistic about it and hope that I can avoid the cost of additional support. I should probably have investigated the 4-series tripod already with the 80-400 AF-S but it does represent 1.2 kg of extra weight and the lens seemed to be a part of the problem not just my tripod. Now I understand it was a combination of factors.
I will try to investigate also how the tripod-based sharpness differs from monopod mounted and hand held to get a feel of how much of a compromise I would make when choosing less support (the advantage of less support is greater mobility and a faster shooting experience). So far it is my impression that the monopod does provide a significant help compared to hand holding this lens, but I'm not really a fluid monopod user, so I'll have to work on it. Mounting the lens on the monopod is a nervous moment for me as I'm used to one component (the tripod) being stable and both hands being free to position the lens while it is being attached. When mounting a heavy lens on a monopod, both are in motion and only one hand is free to support the lens. I really don't want to drop my kit ...