The high ISO performance and no-vibration shutter of the a7S are liberating in many ways. One, which hadn't occurred to me initially, was that I could use slow/long lenses much more effectively.
I have a nice little Minolta AF Reflex 500mm which has been mostly useless without a tripod on the a7R. Since it's a fixed f8, I just couldn't get a fast enough shutter speed at a acceptable ISO, except in full sun. (I live in Minnesota, where full sun is scarce.)
With the a7S, I set the shutter to 1/500 and let auto ISO do its thing. The results have been most gratifying.
Rushes - ISO1000 - 1/500 at f8 - handheld
Disused mailbox - ISO2500 - 1/500 at f8 - handheld