I feel that Bitmain is skimping on the PSU. Assuming that they're using
Enermax ERV1000EWT-G 80 Plus Gold which is approximately 90% efficient at around full load (996W or 83A total on the 12V rail), the S2 would be drawing around 900WDC (1000WAC at the wall*90%) from this PSU. That's a 90% (900W/996W) continuous load 24/7. That's too close for comfort. A 1200W PSU (75% load) would be more appropriate. Personally, I prefer a 1500W PSU (60% load) for the S2; much closer to peak efficiency which is at 50% load.
Bitmain should offer an option to sell the S2 without a power supply at an appropriately reduced price so we could supply our own PSU just like with the S1s or get rid of the relatively puny 1000-Watter and use at least a 1200W premium PSU. The cost difference for them shouldn't be that much especially when purchased in bulk.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817194101I am also concerned about Bitmain's choice of power supply. As a rule of thumb, it's not a good idea to demand more than a 80% continuous load from a PSU. Sustained loads close to the maximum output will decrease power efficiency and significantly reduce the expected operating life.
Your estimates are the same as mine: considering Bitmain's claimed power draw of 1000W at the wall, we can assume that the power supply is operating at around 90% of maximum output. Even if it's operating at just 85% of maximum output, that is still an uncomfortably high level for a continuous load.
I feel that it would have been more prudent to offer a 1200W power supply to keep the load at 70-75% of maximum capacity, or allow customers to select their own. I would appreciate the option to purchase an S2 without a PSU so that I have an opportunity to select a more suitable PSU of my own choice.