https://www.dpreview.com/reviews/ima...44578503921836
Canon 7Dii is $2398 at Digidirect.
Canon 80D is $1498
Canon 6Dii is $2405
Canon 6D is $1777 (slightly better dynamic range than the latest 6Dii. Only advantage of the 6Dii for nightscapes is the variable tilt LCD screen.
Then there is the Nikon d750 (aging but a good performer)
Nikon D810 also a good performer.
You can get full frame sensor cameras for the price of the 7Dii. 7Dii is supposed to have very low read noise. But it must have other components that are somewhat noisy as the DPR studio scene looks fairly clean but not impressive.
Full frame sensors are 1 stop more sensitive to light than APSc due to the collection size of the larger sensor. They typically have 1 stop better dynamic range as well and have a wider field of view for the same focal length.
600D is several models ago whereas 7D2 is the current model.
Greg.