Pi 5 PCIe Gen 3 SSD Performance vs USB 3

What are the Differences between Gen4 and Gen3 PCIe SSDs? m 2 4 0 in 3 0 slot is a slot that can interface with SATA , PCI Express m2_1 slot NVMe drive will get maximum performance in a pcie 4 slot, but I'm trying to get a sense of how the latest drives perform in pcie 3

m2 slot screw USB Gen 2 x 2, USB Gen 1 x 4, USB x 3 (Optional Mini PCIe Slot x 1 Micro SIM Card Slot x 1