Thunderbolt 3 used to be limited to 22gbps as per the technology brief:
and this has been confirmed by many benchmarks over the years. The first benchmarks of native USB4 enclosures show 29.6Gbps which smells like a PCIe 3.0 x4 limitation to me. It's possible the Intel Core i7-1260P used in the test has a PCIe 3.0 x4 connection somewhere between the CPU and the TB4 controller but that's somewhat unlikely given this block diagram from the datasheet which shows the TBT4 controller integrated in the CPU which uses PCIe 4.0 to communicate with the outside world so why would it use a slower one inside:
The SSD is capable of far higher read speeds as well see for example this benchmark. It is of course possible the ASMedia ASM2464PD has a limitation in it somewhere but it's also possible the standard has a limit. So from this test I can't tell what's the USB4 limit: the 40Gbps bus limit or the 31.5Gbps of PCIe 3.0 x4?
