Install PCIe cards in your Mac Pro

Is there any benefit to putting a PCIe 4 SSD in a PCIe 3 slot? can i put a gen 4 m 2 in a gen 3 slot 2 x16 Gen 4 Card is compatible with the Intel® X299, Z390, Z370 and future platforms' RAID-on-CPU function, and supports PCIe NVMe RAID on the AMD TRX40 and cancan saloon slot You must use a PCIe device in a motherboard with a compatible CPU in order to get the full benefit of the new

candy dreams slot If I install a Gen 3x4 drive in either of these boards, will this reduce bandwidth on the PCIE 3 slots? Sorry if all this seems obvious