Recent build problem PCIE x4

Recent build problem PCIE x4 can i put pcie x4 in x16 slot 2 slots with x4 PCIE lanes each can you use ddr5 in ddr4 slot Put in the x16 slot You will lose performance using a x4 slot for sure No real reason to put it in the lower slot, just would look odd

can casinos tighten slot machines There are basically three four different types of PCIe slots: x1, x4, x8, and x16 does it