Both models will output 10-bit N-Log or HDR (HLG) footage to an external recorder, with ProRes RAW supported immediately and Blackmagic RAW, via the Blackmagic Video Assist, coming in February 2021. However, the Z7 II will likely create slightly fuzzier video due to line skipping, so the Z6 II (as with the original Z6) should be a better option for video.
The bodies are largely unchanged from the original Z6 and Z7, with one large exception. Both now come with dual card slots, one for SD UHS II cards and the other for faster XQD or CFexpress cards. That addresses one of the biggest problems with the originals — the lack of a second card slot as a fail-safe for mission-critical shooting.
Shooting speeds are much improved, with the Z6 II now capable of 14 fps for reduced-quality 12-bit RAWs and continuous AF with a single point. More realistically, it can handle 12 fps with subject tracking enabled. Meanwhile, the Z7 II can shoot 10 fps, but also with just a single autofocus point (and no subject tracking) enabled. Still, those speeds are much improved over the previous models, as the Z6 could only handle 5.5 fps with continuous autofocus. Better still, the Z6 II and Z7 II have double the buffer sizes, so you can shoot bursts for twice as long.