Given the same lens (300 f4), which would be a better body to shoot the moon, a Z6 (new, full frame) vs. D5500 (circa 2015, DX).
I am leaning towards Z6 with greater crop in post.
Thanks for any thoughts.
The Z6 has in-camera DX crop, but then you only have 12Mpixels in DX format.
A 300 mm lens at ∞ will project an image on the sensor (any sensor, cropped or not) less than 3 mm in diameter, so you need all the resolution you can get.
Resolution-wise, the D5500 would be the better option.
On the focussing side, it's much easier to focus with the Z6 and its EVF zooming at the press of a button.
Since I assume you have both cameras, you can easily try both to see what best suits you.
The 300mm is a bit short, especially on a FF body, would do fine on a CX size sensor (8.8x13 mm), you probably need to add a teleconverter.
Ciao from Massimo