My cards are RX580 and I need 7 slots
AsRock H110 PRO BTC+ (s1151, Intel H110) with 12 PCi-e 1x + 1 PCi-e 16x
Asus B250 MINING EXPERT (s1151, Intel B250) with 18 PPCi-e 1x + 1 PCi-e 16x and 3 ATX 12v
P.S. Asus B250 MINING EXPERT remains 12 slots for upgrade
From where I sit.... using those "modern" motherboards with bunch of PCI-e slots and put over there all your cards is the same as to put all your eggs in one basket. Besides such boards, full of graphic cards, are quite greedy for power end require costly PSU. So, for me the better option is to have a few rigs equipped with AsRock H110 PRO BTC which, moreover, had shown its reliability.