This thread is fairly well deceased at this point, but OWC recently pushed the shipping date for the Thunderbolt Hub out to early February. They have also listed a new
Thunderbolt Dock for $249—their version of the full-sized Intel Thunderbolt 4 Dock reference design.
Yes, but the upstream is also 40 Gbps. So while each of the 3 downstream can do 40 Gbps (that's for DisplayPort up to 37 Gbps and PCIe up to 22 - 24 Gbps) the total max is also 40 Gbps. This is ok since the computer is not usually transmitting to/from all downstream devices at once.
37 Gbps of DisplayPort is for a XDR display connected to a GPU that does not do DSC (dual HBR3 signals is used instead of HBR2 with DSC). Dual HBR3 usually doesn't work from a dock or hub though. It is unknown if that is true with this OWC Thunderbolt hub (probably?).
34 Gbps of DisplayPort is for dual HBR2 displays which a Thunderbolt dock should be able to do. The highest I've been able to do is dual 4096 x 2304 x 68.595 Hz x 24 bpp = 31 Gbps without a dock (unclear what the overhead is).
Whatever is not used by DisplayPort can be used by PCIe data (and/or USB data in the case of a USB4 compatible hub - it is unknown if the OWC Thunderbolt hub decodes tunnelled USB or if it can be connected to a USB4 host that does not support Thunderbolt).
Titan Ridge and newer Thunderbolt controllers support DisplayPort 1.4 / HBR3, whereas most Thunderbolt 3 docks are based on older Alpine Ridge controllers which are only capable of DisplayPort 1.2 / HBR2. The OWC Thunderbolt Hub uses the Goshen Ridge
JHL8440 Thunderbolt 4 Controller, which can handle DP 1.4, HBR3, and DSC passthrough.
In theory, the JHL8440 supports tunneling for up to 40 Gbit/s (in one direction) of DisplayPort packets, 32 Gbit/s (in both directions) of PCIe packets, and 10 Gbit/s (in both directions) of USB3 packets, with the combined total traffic not exceeding 40 Gbit/s in either direction. Thunderbolt 4 is USB4 plus Thunderbolt 3 interoperability, so yes, this hub will also work with USB4 hosts and devices that do not support Thunderbolt interoperability. Also, both upstream and downstream facing ports on all USB4 docks are required to support Thunderbolt 3 interoperability. Despite OWC's use of the term hub, I believe that both Intel and the USB-IF would classify this device as a dock due to the inclusion of the downstream facing USB Type-A port.
By my calculations, the Apple Pro Display XDR at 60 Hz without DSC requires 38.7 Gbit/s of DisplayPort bandwidth. 4096 x 2304 @ 68.595 Hz, 24 bpp works out to 16.36 Gbit/s which is still under the 17.28 Gbit/s limit of HBR2. Although it's a slightly lower resolution and frame rate, 4096 x 2160 @ 60 Hz, 30 bpp actually uses a bit more bandwidth at 16.7 Gbit/s. To top the Pro Display XDR's bandwidth would require something like a pair of HBR3 capable Gigabyte Aorus FI27Q-P displays at 2560 x 1440, 30 bpp, and 158-162 Hz.
PCIe tunneling to any single Thunderbolt endpoint is limited to the equivalent of a PCIe Gen3 x4 link. Given an 128 B maximum TLP payload size and 16 B TLP headers, that should yield up to 25.92 Gbit/s of throughput after accounting for encoding and protocol overhead. The observed PCIe throughput over Thunderbolt seems to hit a wall at around 21.32 Gbit/s. However, that would mean that at least 25.92 Gbit/s of PCIe packets are being tunneled... which seems an odd coincidence.
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