Is it normal to have only 16% gpu usage on HwInfo ?

i'm getting about 230 Mh/s @ 1000watt ( 4 rx480 + 4 rx 580 )
That's awesome. How is this possible?
My 2x R290 needs 550W for 50Mh/s-cvddc 850
-mvddc 850
they're magic with rx480/580.. not sure with R290 but if they crashes try increasing to 880/900
also the temperature decreases about 30%

"Supports latest AMD 4xx cards only in Windows." :-(
I've done already -100mV via MSI Afterburner...
Ok, now iam sure, I try more undervolting with editing my bios!
The new ATI cards are much more power efficient!