Just ran disk mark against my two drives. Both are hitting their rated speeds at PCIe 3.0 x4. 1TB Samsung PM9A1 (stock main) and 2TB Pioneer APS-SE20Q-2T (added secondary). So it doesn't
Samsung Pm9a1 Ssd Pcie Gen 4.0x4 Nvme Solid State Drive 256gb 512gb 1024gb 2048gb M.2 2280 Internal Ssd For Desktop Laptop - Solid State Drives - AliExpress