You might want to install pkgsrc/ttcp; it's a standard way of doing 
exactly that sort of test.

That said -- how are the two machines interconnected?  I've had similar 
network performance issues when the duplex setting on my NIC disagreed 
with the switch.  To be sure, it was a weird built-in 3Com NIC on a 
Dell machine where I had to disable auto-negotiate (I can dig up the PR 
number if you want), but the net effect was that if I set things 
incorrectly, I could do slow speed network I/O but not high speed.


		--Steve Bellovin, http://www.research.att.com/~smb