Photographing astro and aurora images generally uses a very wide angle, fast lens. Such lenses gain a benefit from using a full-frame sensor. For wildlife, with a FF camera, you will lose some of the telephoto 'boost' effect gained from using a crop sensor. However, the R5, at 45MP is sufficient for most people shooting wildlife, as I do myself.
To see an explanation of the relationship between crop sensor cameras and full-frame ones, and the implications of that, read the following Word document shared from my MS OneDrive:
Equivalence: How sensor size impacts Field of View, Aperture and shutter speed
The questions that should be considered are what kinds of wildlife do you shoot and, most significantly, what kinds of output do you produce.
There are other issues with regards to the performance of the R7 as a wildlife camera body that may, or may not impact you. Those issues are not true of any of the full-frame variants. See this video on the subject:
https://www.youtube.com/watch?v=hsmY4f1J0t8&t=2s
Essentially, the pixel density of the R7 is too high for the focusing system, the sensor (resulting in electronic shutter lag), and the data bus. Lower pixel densities of the full-frame bodies do not have these issues and they have much better focusing systems.
cheers, TREVOR
The mark of good photographer is less what they hold in their hand, it's more what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
