All of our ants @ 393mhz get 200GH/s, and pull 410W at the wall with an 80 Plus Gold 750W Rosewill PSU, which is right at 90% efficient at. That means our Ants are pulling 370W from the PSU, and this includes removing the blue/white wires from the fans so they're running at 100%.
If your 2 ants are pulling 900W, you need a better (more efficient) PSU.
I't was a pretty inexpensive PSU (under $80, possibly under $70) so it may not be the most efficient, good brand but I don't remember at the moment and it's not much of a concern to me right now, I am paying less than 6c per kilowatt of wind energy--it's unlikely I would have gotten ROI on a more efficient power supply and with wind energy--no real reason to feel bad about using a little more.
Either way, it's still necessary to account for both the power supply and the additional energy usage (depending on rate, of course) of the 6 S1's over 1 S2. I'm not suggesting it wouldn't be worth it--but you can't base it off the math that was provided. Also, who knows what the S1s and S2s will be priced at when they bring them back, it's kind of a waste of time and energy to even try to made a decision now without that information.
I definitely plan on playing with frequencies a little more to see if I can get better hashing than with them set to 400Mhz, whenever I have a chance.
It was working for me earlier and it's working now. Also--THEY HAVE S1's IN STOCK!!!!!!!