re: Visible disk
I noticed the other night that both Venus and Jupiter disappeared/rose gradually behind a ridgeline, not instantly like a star would.
Some diligent person could probably do the math to confirm Nick's observation that someone with astute vision could perceive a disk for both planets.
I played with the Solar System Simulator and got a 43.84 second diameter for Jupiter on a close approach with Earth, and 51.77 second diameter for a close approach with Mars. I bet if someone like Nick on Earth observed Callisto rising behind a ridgeline before Jupiter did, Callisto might be visible. Should have several minutes of separation.