pciutils is discussed at
#206 and later. It can be used to get information about a PCIe card, including the current link speed and width, using the PCIe registers. In some cases, a 8.0 GT/s card may have it's speed incorrectly set to 2.5 GT/s in a 5.0 GT/s slot and some pciutils commands can adjust the speed back up to 5.0 GT/s. This problem exists with the amfeltec and GC-TITAN RIDGE when used in the MacPro3,1. Newer Mac Pros get a
new firmware update with Mojave that may fix this.
If you go to the support page for the GC-TITAN RIDGE which was linked in the first post, you can see there are two DisplayPort 1.4 inputs.
The Sunix UPD2018 has only one DisplayPort 1.2 input and can output only USB-C with DisplayPort alt mode (like used by the LG UltraFine 4K). It cannot output two DisplayPort signals plus PCIe over Thunderbolt (like used by the LG UltraFine 5K).
With two DisplayPort 1.4 inputs, the GC-TITAN RIDGE can support two USB-C displays such as the LG UltraFine 4K (but you should also connect the USB 2.0 header to support audio, brightness control, and USB ports of the display). You can transmit two 4K DisplayPort signals using a single Thunderbolt 3 port, or one display (up to 8K 30 Hz) per Thunderbolt 3 port.
The GC-TITAN RIDGE also supports Thunderbolt displays.The LG UltraFine 5K uses two DisplayPort 1.2 signals. Lower resolution Thunderbolt displays only use one DisplayPort signal. Newer Thunderbolt displays (don't exist yet) may use DisplayPort 1.4 which can do 5K with one DisplayPort signal so you could connect a second to the other Thunderbolt port.
UPDATE: dual 8K 30Hz may be too much for the GC-TITAN RIDGE. I haven't seen anyone show that dual HBR3 works. Dual HBR3 is required for the Apple Pro Display XDR 6K display when using GPUs that don't support DSC. USB-C displays that also support Thunderbolt connection (like the newer model LG UltraFine 4K) using a Titan Ridge Thunderbolt controller require PCIe tunnelling over Thunderbolt for USB support. I don't know a method to make such a display connect via USB-C mode instead of Thunderbolt mode.