Gromit
Plasticine Dog
Are you able to buy on sale or return? I think the best way is to get the camera in your hands and see if it works for you. I absolutely love the Z cameras. The bodies are superb and as you say, due to the short flange distance, they can be used with a wide array of lenses. Not only that, but due to the IBIS, you get to shoot these lenses stabilised too (another benefit of mirrorless - it seems only Pentax are doing IBIS in a DSLR body)
Lefty
Shortly after the release of the Z cameras, I did have a brief play with a 6 at LCE in Lincoln which felt so good in-hand The only camera I've picked up which feels as comfortable is the E-M1 Mk2 which is a triumph of ergonomic design IME - how Oly have made a camera fit large hands, yet be so small, is amazing. The Z also has that 'just right' feeling, and Nikon's UI is a given as I'm familiar with it. The store manager at LCE is a good friend of mine so he may (if I ask nicely) get to take a Z6 for a wander for an hour or so. Handy as the shop is only a 5 min...er perhaps 10 min walk (it's up a bloody steep hill) from the Cathedral.