Many factors can affect this.
- Speed of the drive itself
- Other programs accessing the drives at the same time
- Where on the drive the data is located
- Drive fragmentation
- Number of files being transferred ( 1 huge file will go faster than 10000 tiny ones )
I can peak just a bit above 100mb/s on mine but it usually slows down and goes between 40 - 80mb/s after that depending on which drives and going to/from. I'm going between Win7 and Ubuntu.
On Windows7/Vista there's a built-in throttling mechanism.
Because multimedia programs require
more resources, the Windows networking
stack implements a throttling
mechanism to restrict the processing
of non-multimedia network traffic to
10 packets per millisecond.
The throttling will come into effect
only when you are running multimedia
programs that are time sensitive.
However, this throttling mechanism can
potentially cause a decrease in
network performance during the active
multimedia playback period. This
decrease in performance is likely to
occur only on high speed networks that
are saturated to maximum capacity.
There are many things you can try. Its debatable as to how much of a performance boost you'll get. You could try this: http://support.microsoft.com/kb/948066
You can also see if enabling jumbo packets on both machines could help. Larger packets could help. This may or may not help.. Check out the link.