. A PCIe 4.0 graphics card will work in a PCIe 3.0 motherboard slot at PCIe 3.0 speeds. For PCIe 4.0 graphics cards, maximum graphics throughput can only barely exceed that of PCIe 3.0. For this reason, the benefits of upgrading your motherboard to PCIe 4.0 will be minor. PCI-Express versions are backward compatible, meaning that you can use a. Apr 22, 2008 · While this used to be 75 W plus 75 W auxiliary power for PCI Express 1.1, PCIe 2.0 now supports a maximum of up to 300 W when fully implemented on a motherboard. Graphics board designers still.