Welcome to the Community,
Realtek 8168 Gigabit Ethernet - vSphere reports 10MB Full Duplex Auto Negotiate (Read online that this speed doesnt matter as it will perform better?)
The speed on the physical network adapter certainly matters. This is the maximum speed for the host to connect to your network. I guess what you read was about the network speed within a virtual machine, i.e. the virtual adapter!?
André