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 Internal SSD M.2 256GB 512GB 1TB 2TB NVME PCIe 4.0x4 Internal Solid State Disk HDD Hard Drive for Laptop Desktop - AliExpress
Samsung PM9A1 Series 2TB PCI-Express 3.0 x4 (NVMe) M.2 2280 Internal Solid State Drive (SSD)
Amazon.com: New PM9A1 MZ-VL21T0A Solid State Drive 1TB Internal M.2 PCI Express GEN4 X4 OEM for XPS 13 15 17 Yoga 9i 7i Spectre x360 2-in-1 Laptops (1TB Gen 4x4 SSD) : Electronics