A quick update on the Nikon D750 - the camera will be announced in approximately 10 days (around September 11-12th), which is right before the start of the Photokina show (September 16th). I can also confirm the 51 AF points. I have few other specifications that I may publish later today (still trying to confirm them). If you have any additional specs, please contact me.
Update: the actual announcement date will most likely be September 11th, since the 12th is a Friday and Nikon has never made any announcement on a Friday.