use both PCIE x16 gen4 and gen3

All 11th gen and 12th gen and accordingly 500600 series mainboard support PCIE , it's nothing special and not rare Also most GPUs don't

PCIe boards can fit into slots designed for their lane configuration or higher Plugging a x4 PCIe into a x16 slot is acceptable

canadian slot sites slot on a PCIe gen or motherboard is pretty fast As the name implies Can I physically put a 16x card into a 4x or 8x slot? How? Reply Alex

can i put a pcie 40 in a 30 slot  It's not a question of efficiency ( whether or not it's justifiable to use expensive card designed for 16x PCIe in 4x slot of PCIe