Good result. I think the third card isn't performing as the first two because of the RAM. If lolminer is using the RAM to compensate the vRAM missing, maybe at least 16gb RAM are needed, possibly 3200mhz so they are fast.
Thanks, but this is not the memory, somthing else, here is the specs of the MoBo
Expansion Slots:
2 x PCIe 3.0/2.0 x16 (Single at x16, dual at x8/x8, )
1 x PCIe 3.0/2.0 x16 (max at x4 mode, ) - i think that is the reason why the third works on smaller hashpower
3 x PCIe 3.0/2.0 x1