Problems with ethernet speeds

[#1]

I have a desktop and netbook running windows 7, and a new laptop running windows 8. I have all 3 connected to my WNR1000v3 router via Ethernet. The desktop can see speeds nearing the maximum my line can support (about 56MB down and 16MB up).
The laptop and netbook however can only see about 25MB up and 11MB down.
Considering they are all connected to the router by Ethernet, I thought that the speeds should be about the same.
I'd like at least the Windows 8 laptop to be nearer the 56MB speed.
Is this a network card or configuration issue? I have the latest drivers installed for all computers.

[#2]

What are you doing to measure those speeds ?
  Are you running an internet speedtest ?
  or are you measuring the ethernet transfer rate by doing a large file copy on your local network ?

[#3]

running an internet speed test on each computer, unplugging the others. using speedtest.net for measurement

[#4]

on a large file (1.4GB) from the desktop to the win 8 laptop I'm getting about 6.5-7 MB/s

[#5]

In Plusnet speak that's about 70Mbits/sec.
Machine A sends data to router (limit 100Mb/sec),
Router then sends data to machine B (limit 100Mb/sec).
The ports in the router are limited to 100Mb each.
So that is a reasonable performance.

[#6]

Is the netbook using something like an Intel Atom CPU? Sites such as Speedtest give misleading results on my Atom N450-based netbook, as Adobe Flash just eats up all CPU resources and as a result caps the throughput way lower than what is actually possible.

[#7]

Similarly, Windows internet security suites on laptop/notebooks may also cause internet related downloads to effectively be throttled while the file contents are being analyzed.  For the purposes of speed testing, it might be worth switching internet security off and see what happens.

[#8]

Found out the cause of the problem. firstly I thought it was the internet security software. I turned it off and it looked like that did the trick. I looked at the network adaptor settings and found the AppEx Network Accelerator enabled. This was installed by default on my PC as part of the driver installation. I turned this off, re-enabled the Internet Security and re-ran the speed test. Voila I got full speed WITH my Internet Security enabled.