IBM showed me this one to do a FTP transfer test without using the disk subsystems, which will give you a more accurate measurement of the network.
ftp targetserver login bin put "| dd if=/dev/zero bs=32k count=4096" /dev/null
This will put a 128M file and give you some statistics to determine if the speed is ok.
Theorectically, for a 100MB/s network it should go in 10-15 secs, for a 1GB/s network it should be between 1 and 2 seconds, however in reality this rather depends on routing, network devices, network caching, network traffic, etc. So for a 1GB/s network which is well utilised expect a 10-20 sec transfer time anyway.
Using SFTP or SCP introduces the encryption lag, and seems not to saturate the network bandwidth enough to provide valid results.