ASUS PRIME H270-PLUS 109$
MSI H270 TOMAHAWK ARCTIC 125$
ASROCK H270 PRO4 112$
both 1151 socket & 6 PCIe 3 slots (same Offer as Biostar which should be much cheaper), reference price from AMZ
Gonna be hard to drive 6 GPUs from 5 PCIe slots.
Please only recommend boards you know work.
For instance I have a board with 7 PCIe slots and 2 m.2 slots that theoretically could drive 9 GPUs.
Realistically it can only drive 4.
First you cant populate any M.2 with NVMe w/o account for PCIe lines (and PCIe slots), you should use M.2 Sata SSD.
Whatever nobody who want to earn money will put nothing more than a cheap usb3 16gb flashdrive on it, so discard the M.2 interference.
You should setup PCIe to PCIe v2.0 in bios.
Specifications for Asrock H270 Pro4 are wrong at amazon.
but these are verified:
ASUS Prime H270-Plus
>>> 6 PCIe slots: 1:x16 1:x4(x16 slot) 4:x1
https://www.asus.com/Motherboards/PRIME-H270-PLUS/specifications/MSI H270 TOMAHAWK ARCTIC
>>> 6 PCIe slots 3:x16 3:x1
https://www.msi.com/Motherboard/H270-TOMAHAWK-ARCTIC.html#productSpecification-sectionAll based the on Intel H270, better chipset than as Biostar's TB250 H250.
However, I suggest caution to invest on these MoBos as soon will be available cheap PCIe Switches for 8+ GPUs from at least two vendors, one of these seems is regular to bitcointalk.
I am leaning towards Asus but MSi is a good option too.