Most USB PCIe add-on cards are single chipset and the ports share the available bandwidth.
Theoretically, if I have two USB 3.1 Gen I devices that each can saturate the 5Gbps bandwidth, attaching them to a USB 3.1 Gen I add-on card will limit each to 2.5Gbps.
Will attaching two Gen I devices to a Gen II add-on card allow each to run at its full 5Gbps, being Gen II is 10Gbps?