The Seasonic VERTEX GX-1000 wins in 5 out of 9 comparable specs, with 2 ties. Its biggest advantage is 12VHPWR Connector (100% better).
RM850x wins in 2 specs (PCIe Connectors: 50% better).
Recommendation
Choose VERTEX GX-1000 if you want the best overall performance — especially 12vhpwr connector.
Choose RM850x if pcie connectors matters more to you.
