MSI B350 Gaming Plus 5 Pcie /  ryzen 5 1500x /  M.2 ssd 120./win 10 Pro

7 Gpu stable:
3x rx 570
2x rx 580
1x r9 290
1x rx 560

1 Multiplier pcie (4 usb ) =  slots pcie  3.0x16
3 riser usb  = 1( slots pcie 4x) / 2(slost pcie 1x)