Running 6 cards on a onda riserless mobo, 1500w at the wall, 490mh/s.
1575 clock, 860mv, 950 mem phoenix miner.
Something seems to be sucking up power unnecessarily in your setup - I ran same settings but w/ my mem just a touch lower (935), and only saw 215w/card - looks like you're at 240-245 for some reason, which is generally more in-line w/ the 90Mh/s config.
My rig has 4x 4000rpm fans (or 7x 3500rpm fans), just the mobo + fans with no gpu attached is ~140w.
Even so, it's less efficient that yours. Might be my psus hitting 90%+ load, I use the Evga 1600t2.
Ah yeah - I assumed maybe a 30-50w system power draw... Everyone seems to be running celeron systems these days (or ryzen). So sounds like you're closer to 225w/card - more reasonable. And yeah, I benched on an unloaded PC w/ a 1Kw platinum PSU, so possibly a touch higher on the efficiency curve.