Running 6 Vega56@64 @ 850 MHz @ 825mV (850mV for two weaker cards) on core_P7.
Getting approx 98 KH/s combined at 950W at the wall.

That's actually hilarious. This is pretty much roughly 150W per Vega. 103 h/W. L18+18.

L20+20 results in roughly the same figures. More interleave adjusts though.

L22+22 gives a whole bunch of interleave adjusts (all GPUs) and no improvements in hashrate from the values tested above... and ends up crashing after a while.

EDIT: @pbfarmer, I've not managed 18.3 kh/s as you seem to though. More like 16.5 at 850/1107. Using Core_P7 though, not sure that's what's making the difference?