I am trying to decide between a7s vs a7ii for video, so that it can compliment with my stabilizer. Currently use the 5d and c100 and they are too heavy for the stabilizer when doing Weddings. Is it worth paying double for the a7s
The a7S has a better image, whether it's enough of a difference for the price given your needs, you'll have to be the judge of that...
In any case: did the firmware update make IBIS useful for video? There were some awful samples shot with the initial release (IBIS created awful micro-jitters every couple of seconds)