Re speed, looks like the cables are the right ones. Would be nice to find a wiring diagram of the motherboard to see how the pcie lanes are allocated but hard to find on these consumer devices. Perhaps each usb4 port is a single lane gen2 which would top out around 10Gbps. You could try paralleling iperf3 to give you a bit more info. Also check the tx_speed and rx_speed in /sys/bus/thunderbolt/devices to see what it is negotiating.
Company specific TB driver/firmware updates can be found here https://www.thunderbolttechnology.net/updates