The 645D was a pretty solid camera, even if slow as a snail, you'd think it was the year 2000 all over again.
The way the D is so slow to do anything makes its SLR shape rather deceiving, as you can't handle it like one. The Z is pretty much on the spot though, as the faster buffer, shooting speed, AF and better dampening make it very easy to use hand-held.
For landscape it's a fine camera, pair it with the 35mm and away you go, but for portraiture it'll a bit more tricky due to the mentioned reasons.
I only had the D for a few months, as it was on loan from a friend who wanted to sell it, but I kept the lenses and bought a Z afterwards; addition of live view alone made it worth it for me.
But then came the first shots and oh dear that dynamic range. Let's just say I've attempted to capture a few HDRs and ended up not blending them, just one shot with shadow recovery alone was enough.
Images from the 645D were also very good, with punchy colors and contrast, and a very smooth highlight roll-off as with all CCD sensors. Dynamic range wasn't much better than my 5D2, if you attempt to recover shadows too much the noise pops in rather soon, even at base ISO.
With the selection of excellent high-resolution cameras available today, such as the A7RII and 5DSR, the D seems to me like less of a good deal than it used to be, even if you manage to score one for $3000 or less.
Again, I have to emphasize that the 645D is slow, as in 3+ seconds from capturing an image to seeing the preview slow. It felt like forever... Well, better than the speed at which you can see what you shot on film, that for sure!