You will not like the output of the CCD 60 or 80MP backs at 1600 especially if you are working at night. These backs will perform best in their base iso range plus maybe iso stops. By 1600, the amount of noise will be extreme in normal modes, (not sensor plus)
Both Phase One large backs, in the 60 and 80MP size offer sensor plus, which is pixel binning, 4:1, so your 60MP output is 15mp and 20MP from the 80MP. Here you can use 1600, but I don't feel the output will be as good as any current 16 or 20MP camera on the market today. Sensor plus is nice feature but I only use when extreme situations arise.
Inversely, the 50Mp backs, especially the Phase One IQ150/350 and Leaf Credo 50, can easily get to 1600, with no problems and go to 1 hour on a single exposure. You can get around the dark frame exposure (which may not be necessary) by putting the back in aerial mode. You mentioned that you don't want the 1:3 crop so your only real option for 1600 full frame is CCD and for the cost, I don't feel you will like the output.
Paul