I have been using a Canon 7D to record some footage for my degree show piece, and came across this demonstration of noise levels at various ISOs.
Note that the cleanest image is not at ISO 100, as you might expect, but at ISO 160, which is probably the 7D sensor’s native ISO. The video gets progressively noisier for each third of a stop above a multiple of ISO 160. This leaves your options at 160, 320, 640, and 1250. I used ISO 320 for yesterday’s shoot.