I did some benchmarking a while back:
The PCIe 4 lanes are via chipset, while the the PCIe 5 lanes were CPU-connected. Anything else unspecified would also be CPU-connected.
Something more recent I also posted on L1T:
:sadface: I don’t think I have ever hit anywhere near 400 MB/s with queue depth 1 random 4 KiB reads. My fio results hover around 300~340 MB/s.