1210 watts quoted "at the wall" - an EVGA 1300 would have about 10% power reserve, even my favorite Seasonic X1250s have some power in reserve.
Indeed. Some of the more common official peak ratings are in my PSU guide, although for 24/7 its still going to officially be the stated rating. That being said, I've ran many corsair PSUs past their limits in challenging conditions and they've done fine.
Only if you can run each board on two instead of three connectors, contrary to bitmains instructions.
However, they said to use two connectors per board for S5 and some people used just one successfully (with a good quality connector such that found in EVGA).
I'm using an EVGA G2 gold 1300 now with two S5s and it's running at roughly 93/94% efficiency. Per my 'at the wall' meter.
, vertical strato setup with a box fan. I just checked this. Was running at like 97% efficiency when only was running one
, but lot less load.