I have 4 ring terminals on each screw. I'm using 4 of these for a rig:

Don't you lose most of the benefit of distributing the load across many more wires if you don't use all 6 wires from each PCIe connector? Your photo looks like you're only using one + and one GND from the PCIe connector.
No, each splice has three 18 gauge wires (with extra thick insulation) from the PCIe plug on one end and one 12 gauge wire on the other end.
