I just wanted to report my successful bifurcation of the PCI-E 8X Slot into two PCI-E X4 buses! I used a Supermicro RSC-R2UU-2E4R 2U PCIE 8X to 4X4X adapter and now I am using both slot and M.2 onboard connection at full 4X PCI-E bandwidth!! 
I just wanted to report my successful bifurcation of the PCI-E 8X Slot into two PCI-E X4 buses! I used a Supermicro RSC-R2UU-2E4R 2U PCIE 8X to 4X4X adapter and now I am using both slot and M.2 onboard connection at full 4X PCI-E bandwidth!!