To test the available bandwidth between two Windows, Unix or Mac computers, without having the obvious bottleneck that harddrives are, iPerf is here to help.
Start one machine as server, and the other as host:
Server
iperf -s
Client
iperf -c <target ip address> -f m -l 60000 -t 20 -i 5
More info about iperf: http://openmaniak.com/iperf.php