When you want to test the connection speed between 2 server machines you can setup in both machines the iperf package
sudo apt-get install iperf
Then in first server run
iperf -s
and in second server
Iperf -c <1st Server IP Address>
The iperf command uses by default the port 5001, so you have to open it in firewall. If you run this command you will get info about the bandwidth