Perhaps I'm missing something, but that setup does not seem very safe. I have (4) Antminer S1's all overclocked to 393.75 mhz and each Ant uses about 406watts at the wall. The 400mhz setting uses even more power, so even with my conservative power numbers, you're pulling at least 1218 watts out of a 1250w max load PSU. This is a recipe for a disaster.

PSUs are rated by their DC output, not by their AC input. If you're running at 90% efficiency that means with 406W at the wall you're putting out 365W. As a reference, I just tossed a meter on one of mine running at 400MHz and it's pulling 31.5A at 11.92V. That will be running that supply close to it's max at 400MHz, but with 104A on its 12V rail it will probably be fine.