Bought a new setup. G3900 cpu, 4gb ram and a 6x RX580s

Flashed bios and added some small clocks

I get 30mhs on 2 cards when alone in the machine.

Once I add another 2 cards,  all drop back to 27.

I am using claymore,  ethos and have a 1300W PSU

Anybody else had similar? How can I check if im bound by cpu or memory?