https://forums.hardwarezone.com.sg/...5gbps-10-gbps-enhanced.7030365/post-154448683
Just sharing: if i use a 5 Gbps PCIe Realtek RTL8126 chipset NIC, Windows shows the connection as 5Gbps. But I can only achieve around 3Gbps speed download and uploaded on speedtest.net. I am not sure if this is the limitation on my motherboard's PCIe slot, e.g. insufficient PCIe lanes (it is a PCIe 3.0 x1 slot) or the chipset itself. But this is not important, i can use the Intel 10Gbps NIC.
*Update: i moved the Realtek from the PCIe x1 slot to the motherboard's second PCIe x16 slot (which will run in 8x mode as the GPU is already connected) - it made no difference.
On the same PCIe slot, with the OEM Intel X540-AT2 connected, i could achieve the full 5Gbps speed.
My suspicion is that the RTL8126 chipset may have some limitation, though i read online that some people are able to achieve 5Gbps with it.