Did you sign the sys file before adding the rest of the cards in your rig ?
If you change anything in your setup like adding or removing cards you have to sign it again.
Your 480s should do 29Mhs even if they are mixed with other cards.
And to Cintronix:
I've used this one: 480lowenergyOK.rom
I've added all cards and afterwards replace the file and signed it.
When I've started mixed card's rig cards gave me 29.2MHs, but when I tried to reduce voltage on r9 390 all rx 480 dropped to 25.2MHs
Any other manipulations I performed did not resulted in any progress