firstone,
All of the Ethernet shields from Arduino, including the latest R3 shield use the WIZnet 5100. This chip is quite old and due to the way it was constructed the SPI speed is very slow resulting in what I would describe as just utterly terrible performance.
One of my first sketches was to output a JPEG over http stored on a SD card plugged into the Arduino Ethernet R3. A 62 KB JPEG took over 3 seconds for the Arduino UNO with the shield to send the data to the browser which I timed using a Firefox add-on called Firebug. The performance was very slow, it almost reminded me of dialup days or when I first used an ISDN line.
It's going to take quite some time for another Due compatible board to come out that breaks out the SAM3X8E pins and allows you to hook up an external PHY and additional time for someone to develop the code to run a TCP/IP stack.
mantoui,
I have several WIZnet 5200 and even some WIZnet 5300 chips in the mail as well as the integrated WIZ820io which contains a MagJack and the W5200 chip. Once I receive them, I would be happy to run your benchmarks posted and confirm your findings. If what your benchmarks show is true, we may finally be able to get acceptable Ethernet performance out of an Arduino platform running these newer chips from WIZnet.