can we install PCIE x16 graphics card in PCIE

It'll surely be a bottleneck if you're using a PCIe or card in a PCIe slot Simply because the slot doesn't have enough

2 slot With the channel of PCI-E X4, the speed will be enhanced up to 80 Gbps, 5000+ MBs random Read

pcie 4 gpu in pcie 3 slot Yes, PCIe standards are thankfully backwards compatible, meaning that a PCIe device will work in a PCIe slot, but it will only be able to reach PCIe

pcie slot qrelease PCIe is backward compatible with PCIe and PCIe , meaning that PCIe devices can be used in PCIe slots, although they will