I had a chance to play with the D5 at a local photography expo on Saturday and there was not much of a crowd so I could try various things out. It had the 300/4 PF mounted and I tried various autofocus settings.
The cross type sensor points now extend to a large area of the frame and autofocus works extremely well even with the outer areas of the frame, close to the end of the long axis. This is very important to me since I often make full body or half body images of people in vertical orientation and I need to focus on the face. With Multi-CAM 3500 cameras this is a somewhat compromised proposition as the linear points don't pick on facial detail very reliably (unless there is a beard) and so often it is the hair that is focused on, or the focus is off. I've put up with this for many years because there wasn't anything better available from Nikon. Now the focus points extend further along the long axis of the frame so I can position the face close to the top and as the focus using a single point is snappy and reliable. Also tracking works well. I tried multipoint whizbang modes as well where you just point the camera at something, it'll find the face and keep it in focus while the subject is moving towards the camera or to other areas of the frame. This was very impressive, but I suspect I will stick with single point and group AF for the most part, out of habit.
The viewfinder ease of use with glasses is "okay" but not as good as the D3X (in my opinion). It is a bit easier to use than the D810 viewfinder because of the recessed ocular so there is no need to press one's nose against the camera. But I would like to see greater eyepoint. I'm disappointed that they didn't make the whole viewfinder interchangeable with more eyeglass friendly options available. Today I find the D750's viewfinder the easiest to use (especially if taking the rubber eyecup out) of the FX models, but it is not my favorite body in other ways (too small for my hands). I think the D5 will be ok to use with glasses on but I would prefer if they improved this aspect instead of starting out with the best eyepoint in the F3HP and gradually making things more difficult for this not very small minority of users.
The D5 is fairly loud, so it's probably not the best choice for quiet classical concerts indoors, but it's to be expected because of the 12fps capability. High speed continuous capture at 12fps seemed to work well and AF seemed to be doing its job for the needs of an f/4 telephoto anyway. I will have to test this further to see how it works at wider apertures when tracking approaching subjects. I'm very happy with the AF sensor's extended area of coverage along the long axis - this will be a huge help e.g. when capturing athletes if I want best focus to be on the face instead of their torso.
I also tried the D500 and its 10fps continuous capture mode seemed to be quieter than that of the D5, which is understandable given the smaller shutter and mirror, and lower maximum fps rate. 10fps seemed very fast also. I really liked the ergonomics of the D500 and it seemed to have a much better body shape design than the D7100 which is the DX camera I've used last. But I've got big hands and long fingers so it may have something to do with my opinion. I felt Nikon had really gone all out on the design of the D500, so I'm not surprised if it will be very popular.
I think the camera that could benefit the most from the new AF system is the D810's successor, so I would expect Nikon to announce one later this year. With a high resolution sensor, the added AF reliability is even more important than with a moderate resolution action camera IMO (not saying it's not important in the D5 or D500; it is). However, while I recognize and love the D810's image quality I'm so fed up with the large files (I shoot a lot of frames when photographing people and events, one reason for this is to get added confidence of some frames in focus; maybe with the next gen AF it will not be necessary) that I'm not really looking towards that camera be it called D820 or something else. I fear they may increase the file size even higher than it is now. While the liberal cropping possibilities (frame loose, shoot, tighten precisely in post) of the D810 are useful, I still need something that makes editing large numbers of shots faster for everyday people/event photography.
