USB 2 is 480 Mb/s, not 480 MB/s. 480 Mb/s is 60 MB/s, so the 500 MB/s from PCIe 2.0 x 1 is quite a bit faster and is about the limit of what a SATA 3 interface could do. Also, sequential throughput isn’t nearly as important as most people think. Random IO, which NVMe drives excel at will make a far more noticeable impact on real world performance.