Thanks.
I happened to be near the camera shop on my day's errands so I stopped in; I'd stuffed my Nikkor 50/1.2 AI-S in the bag just in case. Lucky me: the Nikon Rep was there showing off all the latest Nikon gear. I got to play with the Df and D750 quite a bit, had a nice chat with the rep.
AI series lenses work fine, no problem at all, on both. The Df has the movable tab so that Pre-AI lenses can work on it without modification as well. For the D750, I'd have to have my Micro-Nikkor 55mm and Nikkor-H 85mm converted to AI.
Between the two, I much prefer the control layout, feel, and balance of the D750. The Df goes overboard with too darn many knobs, dials, buttons, switches, etc. It's better looking in black than chrome, but it is a weird, messy hodge-podge of styling elements and control paradigms to me.
The D750 is simpler, modern, clean and feels better in the hand. It reminds me to some degree of the Olympus E-1, which I account as the most ergonomic, finest SLR body design of all time.
Neither of them, however, appeal to me all that much. As I told the rep, I shot with Nikon gear from '68 to '01, but what I used from '81 on were the FM, FM2n, FE2, and F3. All the later pro and semi-pro bodies gave me a headache until the D200 came out, when they started to improve again. The D750 is a fine camera, but it's not something I want to spend my money on.
One thing the Rep had that did surprise me was the Nikon 1 V3. He had it on the counter fitted with the 10-30mm lens, grip and EVF. A delightful little piece: felt tight, well made, controls all in the right places, lovely EVF, fast focusing, etc. I was quite taken with it. Hmmm.
G