External SSD link width problem

Mac (Retina 5K, 27-inch, Late 2014)

11.4 Big Sur

Now I am using an AKiTiO Thunder 2 Box with an INTEL 750 PCIe SSD as external hard drive to boot the macOS.

But the I/O performance is really disappointing, the link speed is only 5.0 GT/s and width is x2.

According to https://www.akitio.com/blog/articles/nvm..., the performance should be much better.

I tried reset PRAM but no luck. Help me please.