If you assume the effective shutter time for the iconoscope was 1/60 second, and lighting of 1800 foot candles, and also guessing that the max lens aperture was f/4, this calculates to an equivalent film speed of ASA/ISO 14. The Technicolor process started with an equivalent ISO rating of about 5.
http://www.widescreenmuseum.com/oldc...chnicolor6.htm
This was later increased with improved film stock and eventually with dichroic mirrors in the optics, but it's not clear from what i can find on the web if it got much beyond ISO 25 or so.