5DIII: maximum ISO with HD video?

Anyone know this? With my 5DII I can only use the first expansion (ISO 12800). The 2nd expansion of ISO 25600 I can only use for stills.

The 5DIII base ISO goes up to ISO 25600, so I expect the HD video to go up to the expanded ISO 51200, and with any luck the whopping 102400 will also be possible with video.

But I suppose the excess heat on the sensor caused by video may limit this, maybe even 25600 is the limit (and even then we'd have to be careful not to record more than a few minutes at a time, to avoid over-heating).

Anyone know more?