my FlowerP platinum 1300W burns only 550W at stock S5
yeah but what happens is the second unit will get near the top of the psu and efficiency drops a bit.
I can be almost perfectly certain if you ran 2 at the same settings you will be higher then 1100 watts.
I have done this with
seasonic plat 1200
evga 1300 g2
evga 1600 p2
all of them drop efficiency near 1100 -1150 watts.
I am on 120 volt circuit. if I was on 220 volt most likely I would do a bit better. near the top end.
Right now I have 2 sp20's on the evga 1600 p2 they are doing 1240 + 11110 gh = 2350 gh at 1220 watts. If I run one of the two take the watts . then run the other one of the two take the watts they are at 1195 but run at the same time they use 1220 watts so I lose 25 watts due to high draw.
To be fair it is a 120 volt line.