Not sure where you're getting the 4 from, as only 1 pin will be delivering the power, so on a dual molex to 6pin pcie adapter, it will be 195w/16.25A per board, and 65w/5.416A per PCIe pin, but on the molex side 1 12v pin will be pulling 130w/10.83A.

Get them cheap and use 2 adapters per board to split it out if possible.

Or do what Xer0 said below .

At least you won't have "wasted"/unused wattage per psu, as you can share the current between psu's.