Recent build problem PCIE x4

You can use a PCIe x1 card, or a PCIe x4 card in a PCIe x16 slot They work fine So if you think you are short of PCI-e slots, you may not be

Gen isn't upgradeable on PCIe slots speedstep

can i use a pcie 40 nvme in a 30 slot You can insert a PCIe x1 card into a PCIe x16 slot, but that card will receive less bandwidth Similarly, you can insert a PCIe x8 card into a

can i use a pcie 40 gpu in a 30 slot Here is AMD's Crossfire compatibility chart to help you understand which cards will work together in crossfire and yes x16 and x4 will work fine