Yesterday I got a chance to test 10bit recording using crop module with 5D3 with firmware v.123
Lens 100-400 mm II
ISO between 200 and 3200.
First two scenes recorded at 60 fps at 1920x648 other shots recorded at 1920x1080 30 fps.
Hand held.
Magic Firmware: magiclantern-crop3x.2017Jan13.5D3123
Crop Rec download for testing here: https://builds.magiclantern.fm/experiments.html
Lovely. Crop mode really shines for this kind of shooting.