VPN Adapter: Link Speed settings - related to actual performance?

[nobody12]

I am not sure about this, but I made a few tests and the result is (windows):
If I leave the VPN adapters link speed at the default which is 100MBits/s, I will get worse performance compared to copying a testfile to my PC connected to the VPN if I set the link speed to 1Gbit/s.
With 100Mbit/s I get around 9MBytes/s, with link sped set to 1000Mbits/s I get 15MBytes/s.
The Servers side has a fiber connection which is able to supply up to 10Gbits/s, but in reality it is about 3gbit/s.

Is it correct that the link speed of the adapter truncates the throughput of the adapter? If yes, why is the link speed set to 100Mbit as default? Are there any problems to expect if I set the Link speed to 1Gbit/s as default?