Marc,
Yes, I think there is probably high hopes with the Nikon Mirrorless AF firmware update coming.
As far as I understand the physics and engineering of it, the actual ultimate limits of Mirrorless AF mechanics and communication pathways of Mirrorless lenses (and perhaps even adapted DSLR lenses on Mirrorless) are superior to DSLR. It's only a matter of manufacturers getting their processing capabilities, algorithms and software together, along with better EVF's and operating protocols for them to take the lead (protective market positioning of the next DSLR flagship D6 notwithstanding).
There's no way Canon and Nikon will risk the 2020 Olympics on a mirrorless flagship camera, whereas Sony is on A9ii and might get some traction (and they promise "revolutionary" features). But I think after that, it will be almost all mirrorless.
My understanding is like yours, the shorter flange length is just better for lenses, especially shorter focal lengths. There's also details about the thickness of the sensor glass, which is often what makes hybrid shooting not so great.
With you having (or had) a variety of the top Nikon combinations contenders, you are well placed to comment on the following:-
As I understand it, bodywise, the AF pecking order goes: D5, D500, D850, others .....
I have not used the d5, but it is supposed to be the tops. I personally don't notice much difference between the d500 and d850. They both AF in near darkness (at least in center position). The main thing, I think, is that on the d500 the AF points cover almost the whole sensor while on the d850 it does not cover a lot of the vertical. They are both the "Multi-CAM 20K" type autofocus system (which is same as d5).
I believe the d7500 has the "Multi-CAM 3500 II" autofocus system, same as d7200.
The d5 and d500 will do 200 image bursts at 12 FPS and 10 FPS (continuous AF and exposure), respectively. Thd d850 is only 51 consecutive (but much larger) images at 7 FPS (EN-15 battery) or 9 FPS (EN-EL18 battery). The 51 image buffer has not been a problem for me as I rarely spray for long. 7 FPS is noticeably slower and you will miss some action shots. I really noticed it when I switched from d500 to d850. With the high-power grip, at 9 FPS, it's not a big difference.
The d850 can do a 30fps continuous DX (jpeg) format live-view "silent" shooting (SL2 mode), with fixed focus and exposure, possible banding under some lighting conditions, and moving subjects can appear distorted. I'm not sure what the max buffer is for that, it might be huge as the images are much smaller. You can also do SL1 that allows FX raw images but that's capped at 6 FPS. The d850 silent mode has some features I don't like, but it's really nice when you want it. I use it when I'm expecting motion from a stationary subject, such as a heron hunting in a field or a perching bird about to take off. Definitely not to be confused with the A9's 20 FPS.
Likewise, for the (prosumer) lenses we are considering, (on something like a D500 body for practicality and realism sake) it goes: PF 500, Tammy G2, Siggy Sport (150-600), Siggy Sport (60-600), Nikki 200-500, others .....
I have not used the Siggy's, but from reviews I have not heard of different IQ performance between the Sport and Contemporary.
On a DSLR, I would order like you have: PF 500, Tammy 150-600, ..., Nik 200-500.
I have not used the 200-500 in a long time, so my recollection of its speed might be a little fuzzy. When I got the Tammy, I sold the 200-500. The 200-500 is very bulky. The tammy is more compact, gives great photos, and has more reach. Given enough light, the AF performance on the Tammy and 200-500 is probably pretty close, but like I said, this gets a bit fuzzy for my memory.
What is your experience for AF speed/ accuracy on the same DSLR body between the PF 500 and the Tammy G2 ...... ? :cat:
I
reported here some informal tests between the PF 500 and G2. In a nutshell: the PF 500 is noticeably faster than the G2 under the same lighting. I tested in slightly overcast settings, not in super bright light. So I am not totally sure if this is an f/6.3 vs f/5.6 issue, or how much that contributes to it. When using the PF500 in the field (not at home side-by-side with the G2), I've found the AF to be very good and very fast. It is not instant like the 70-200 f2.8 or 400 f2.8, but it's very fast.
In all likelihood, I'll be selling the Tammy G2 soon.
I have been getting excellent results on the d850 (after AF fine-tune) with the PF 500 and PF 500 + 1.4e3 TC. The claimed 4-stops VR seems to be true. I've hand-held the 700mm at under 1/100th on still subjects. The main issue is an f/5.6 lens + TC will only have 25 cross sensor in the center of the image, and then the others only along the horizontal. As long as you are somewhat aware of where your limited focus points are, you can get good results.
Basically, a f/4 + 1.4x TC or a f/2.8 + 2x TC will have almost twice the number of cross sensors (45 vs 25) compared to a f/5.6 + 1.4x TC. They will also retain 3d tracking. But they are super expensive and heavy.
Marc