According to this post :
https://bitcointalk.org/index.php?topic=526060.0
(S1 undervolt to ~160watt but keep 140 GH speed)
And S2 have same chip like S1 (according to sushi review)

Than I was thinking if an S2 is undervolt of (maybe) 6 S1 with better design PCB so it can do 166GH and 166watt so total 1TH with 1000watt with less heat... If thats right I asume it can stabilized in 1080 GH with 1080 watt (heat like normal S1) OR overclocked to 1200 GH with 1200 watt. And with including PSU people would never thinking buy another PSU so no one overclocking it means less RMA.

Dont get me wrong, Im S1 miner and its a fine product (and delivery too) so I really looking forward to S2 product. But still need to see any review before ordering...