Network Speed issues on Fedora 12

[alan]

I have a couple of systems with gigabit ethernet cards. If I copy a large 
quantity of data to the machine I notice the data throughput start to fall 
off after about 4-5 gigs. It keeps getting slower and slower the more data 
that flows through the interface.

This happens on x86_64 and i386. A similar Ubuntu system does not show the 
problem.

If I run the Fedora 12 system under VMWare, I still see the problem. 
Windows Server 2008 runs fine on the same VMWare server.

Any ideas here? This has been driving me mad and I have seen nothing 
useful on this issue in my various Google searches.

Thanks!

-- 
Truth is stranger than fiction because fiction has to make sense.