pcie x8 in x4 slot: 10 Things That Can Be Plugged in PCIe Slots - PC Guide 101. Mainboard ASROCK B550M PRO4 (AMD B550, Socket .... pci express - PCIe x8 NIC in PCIe x16 slot - Server Fault. Build Your Own - Custom HP Z8 G4 Workstation (2 ....
PCIe 3.0 or PCIe 2.0 x4, x8, or x16
slot; M Key PCIe M.2 NMVe SSD (2230/2242/2260/2280mm).
Up to 128GB Unbuffered ECC UDIMM, DDR4-3200MHz, in 4 DIMM
slots; 1 PCIe 4.0 x8, 1 PCIe 4.0 x8 (in x16 slot), 1 PCIe 4.0 x4 (in x8 slot)1 PCIe 3.0 x2 (in x4 slot)
But I still am unclear about putting a PCIe x8 card in a x4 slot. Sounds like you can but it will run slower.
Slot 1: PCIe Gen3 x4 – Transforms to PCIe Gen3 x8 when 2nd CPU is installed Slot 2: PCIe Gen3 x16 Slot 3: PCIe Gen3 x16 – Available ONLY when 2nd processor ...