you can give iperf3 a try https://iperf.fr/
in cli of the server you can just install it by apt-get and windows from the link
just start the server on one site like "iperf3 -s" and on the other site you will use "iperf -c 192.168.178.10" (change ip to your enviorment)
run some tests, and do it the other way - wat was client will now server and the server connect to this
so you got a clear statement of what is possible.
file transfair strong depend on files - 2tb smal files like config files or documents need much more time than a movie with 2tb.
hope it helps
Thanks for all the input.
During the last days I discovered faster speeds if I am at a specific spot in the house...so the wlan connection needs to be optimized
@draddy, thanks for the tip. I managed to install iperf3. But how do I start it on the server? I tried just "iperf3 -s" on the commandline - but I get "command not found". Do I need to restart the server?
Thanks for more ideas.
But overall it seems that the speeds are OK for a not really optimized system